Reward credit cards work just like any other credit card; you use credit to make purchases or transfer debt, and if you don't manage to pay all the debt you've put on the card within a month, you are charged interest. If you don't manage to make at least a minimum payment every month, you will also likely be charged a penalty fee, and may lose any special offers you've been enjoying.
Therefore, to get the most from a reward credit card, you will want to minimise the above-mentioned costs. This means paying the card debt off every month, avoiding using the card abroad, and not taking money out using your plastic friend. You'll also want to try and maximise the rewards you are getting from the card provider.
For credit cards that offer cashback as a reward (and please note that we have a separate chart with only cashback cards if that's all you're interested in), this means using the card to make purchases as much as possible, potentially even until you reach your credit limit, assuming you're getting a percentage back on every single purchase. If you pick a card with points instead, find out where you can get the most points as well as how you can spend them. While some cards will allow you to get cash in exchange for points, some may only give you vouchers to spend in their stores or petrol stations, so read the terms and conditions carefully.
Where a card offers points as a reward for spending, it's important you check how much the points are worth as well. Points schemes vary massively in value, so don't assume that if you earn four points per £1 spent, it's necessarily going to be better than a card offering one point per £1 spent.
Say you're comparing two cards that allow you to earn one point for every £1 you spend. With Card A you need to collect 1,000 points to earn a £5 voucher, and with Card B you just need to earn 500 points to get a £5 voucher. Although both cards appear to offer the same deal, Card B offers the more generous reward scheme.