Tip #1 - Grab a disposable
If you are still using disposable pads then find the ones you like the best and get ready to examine them. Grab a ruler or measuring tape and measure how long the pad is from end to end. Think about when you are wearing the pads, are they long enough? Are they too long? If the pad isn't exactly right, try to find a measurement of what length you would ideally like in a pad. Make sure you write that number down.
Now look at the width of the ends of the pad. Do they flare out at all? if so, do you like or need that extra width? Measure how wide it is at it's widest point. If you would like it wider or narrower, make note of how much you would like extra. Now look at the width of the crotch part, do you find that a comfortable width, is it too wide or not wide enough. As wings on a disposable can usually be adjusted to wrap around as tight or loose as you like, it is hard to get an exact measurement of how wide a disposable pad is, but you can get an idea.
Once you have looked at the measurements of the disposable pad, you can start to look for cloth pads that are the same basic length or shape, or ones that are the shape you would like to have. When you are thinking of buying pads, keep those measurements in mind. While you are browsing pad listings, have a tape measure with you. When you see a pad you like, look at the tape measure and see how that size actually looks. Don't be afraid to put the tape measure against you (or your undies) and see how that size will fit on your body. If a pad listing doesn't give all the measurements, ask the seller for them (but they should list them!)
Tip #2 - Look at your undies
Grab a pair of your underpants that you'd commonly wear during your period. Now, with disposables, the common thing to do is wear your daggiest pair with the crummy elastic.... cloth pads need snug fitting underpants (not too tight, but well fitting so they hold the pad securely against you) - so throw out your old saggy baggy undies and use good ones. Now... Measure the width of the crotch of the underpants. This can help you work out how wide you will want your cloth pads to be. Keeping in mind that often the fabric in the crotch of underpants gathers up when on your body, so if it's quite wide you might find that a pad of a similar width would feel too bulky. However, if the crotch of your underpants is very narrow, you will find that pads can slip around if they don't fasten tight enough (if the pad snaps wider than the underpants). Also look at the shape of the underpants. If your underpants don't have a lot of fabric in the buttocks, then a wide flared back pad may poke out of your underpants. So keep that in mind.
The width for cloth pads usually ranges from around 2.25" (6cm) to 3" (8cm), although you can also get narrower and wider pads. Generally speaking, the width of the pad when it's snapped should not be wider than the width of your underpants, but it can be smaller. If you are a larger lady, and your thighs touch, you may find a narrower pad won't feel as bulky. If you wear a pad that is too wide for the underpants, not only can it feel bulky, but it also won't be held as firmly in the underpants and can slip around.
Pads that have more than one snap setting will allow you to adjust them to suit different widths of underpants. Some sellers will add another snap setting if theirs doesn't come with one, so always check.
Tip #3 - Waterproofing or not
This is one of the main decisions, and it really comes down to 2 main things. Personal choice and what your flow is like. As there is a vast difference in how much an "average" woman bleeds, what works for one woman might not work for someone else. Unfortunately some people make broad statements about nobody needing waterproofing and so on, but it really depends on your flow.
If your flow is lighter and spreads out more over the pad. Then you can probably wear pads without waterproofing, or with fleece or wool, as your flow has more time to soak in and dry out in the pad. If your flow is heavier, gushy and/or soaks into a smaller area of the pad, then you may find that you need waterproofing of some kind, and may need PUL, because the blood may flow too quickly for the pad to absorb it all. All pads should be changed regularly, but if you are unable to do so (as you work/study), then you may want to look at pads that can hold a greater amount of flow. If you can change regularly, then you may not need pads with a high absorbency.
Of course the absorbency of the pad is the main thing that will determine how effective the pad will be, and this is one of the advantages with a waterproofed pad. If a pad does not have enough absorbent material in it to absorb your flow, you will start to leak through if a pad has no waterproofing. A pad with some form of leak protection will be able to hold more of the flow without leaking. Because of this, pads with PUL can be quite a lot thinner than a pad without it, as fewer layers are needed to hold the same amount of flow. It is also important to choose the appropriate fabrics for your level of flow.
Tip #4 - Fabrics
Fabrics play a huge part of a cloth pad, naturally. Understanding the differences in fabrics used in making pads can help you choose the pads that will work best for you. Common fabrics used as the absorbent core part of the pad are flannel, hemp, bamboo and zorb. Generally speaking, hemp is more absorbent than cotton, bamboo is more absorbent than hemp, and zorb/microfibre is more absorbent than bamboo. Of course the amount a particular pad will absorb depends on the thickness of the fabric and how many layers is used. If you have a medium to heavy flow, you are best looking for pads containing hemp, bamboo or microfibre/zorb. pads containing "batting" or polyester fleece as the absorbent core should be avoided, as they are not suitable fabrics for pad cores. Similarly, flannel is absorbent, but many layers need to be used to achieve the same level of absorbency as a cotton terry or a hemp or bamboo fabric. So pads made of just flannel aren't usually as absorbent as other options.
Top fabrics come down again to personal preference and your flow. Generally speaking, the more textured a fabric is, the quicker it will absorb the flow, so if you have a heavy or gushy flow, you might find a velour, sherpa, minky or terry topped pad is more effective than a flannel or printed cotton top. As well as trapping the flow, the more fluffy the fabric the more it can trap heat, so flatter fabrics can feel cooler on a hot day. But on the otherhand, they can also feel more "wet". Some women prefer to avoid synthetic fabrics (such as minky or suedecloth) because they are not as breathable as natural ones. While it might seem like a synthetic fabric will not work as a top layer, as they aren't absorbent in the way a natural fibre is, on a pad, the flow passes through a synthetic top and into the core, so they can often feel drier than a natural fabric and are less likely to stain.
It is a good idea to try pads with a range of different fabrics, so that you can find out what feels best for you. You may find you prefer different materials on different days, depending on the weather and how heavy your flow is.
Tip #5 - Price
Of course it's tempting to just go for the cheapest option, but sometimes you do get what you pay for, and buying something that is cheap is not cost effective if it doesn't actually work well for you and you have to buy something to replace it. Cloth pads are an investment, they are more expensive per pad than a disposable, but with proper care, a well made pad should last you many years. If you scrimp and buy lower quality pads, you may find they wear out quicker, which is false economy. And while you might be looking for a bargain, keep in mind that pad makers are doing this as their job, so buying cloth pads can help keep women in business!
Often the cheaper the pad, the less absorbent it is. A pantyliner for example will be cheaper than a pad, because it is made to be less absorbent and it is probably smaller, but it would be unwise to buy just pantyliners because they are cheaper than pads - they might not do the job well enough. There is less fabric in it, so it is cheaper. So when looking at the prices of pads, keep in mind the fabrics that go into it, the workmanship and how it looks.
If you are on a budget (and there is nothing wrong with that) some ways to lower the cost while still getting a good product are to buy your pads in stages - rather than trying to buy lots at once, buy one every month as you can afford them. Take advantage of any freebies padmakers give away to boost your stash (such as PIMP) Look for pads that are made from good quality reclaimed/recycled fabrics. Look for second hand pads (often sold cheaply on Cloth Pads) .
Finally, buying pads in discounted sets can be a good way to save a few dollars on pads and postage, but they are only good value if you want all the pads in the set, and if those pads will work for you. Sometimes it might be better to buy one full price pad to see if you like it, then go back and buy more in a set. The other thing to consider is that it is a good idea to try several different brands and then go back and buy more of the brands you like, as not all pads will suit everyone, and you don't want to be stuck with a whole bunch of pads you don't like.