Start with the fine print: read about how points are collected and when they expire. For example, some rewards programs will only give you points as you pay off your balance. Consider starting a spreadsheet that you can enter this information into. As a rule, you get one point per dollar spent, roughly equivalent to a penny.
Next, look at what gets you the most points. Some cards offer more points for gas, groceries or other day-to-day expenses while others offer more points for entertainment or purchases with a specific retailer. Get a sense of what cards will earn you the most for each purchase.
Look at the rewards available on each card. Are they rewards that you're going to use or would like to have? There's no point in subscribing to a rewards program if you're not going to enjoy any of the rewards you earn.
Plan your finances to use the cards enough to get meaningful rewards, but also to avoid racking up a balance you can't pay. Savvy budgeters actually use credit cards with good rewards programs to rack up as many points as possible, and then pay off the balances at the end of the month. This requires strict budgeting and careful planning, however.