Make a plan. A good plan is essential to a successful paver project. Think about where you want your path, driveway, or patio, and then use graph paper to make a scaled drawing of the immediate area. Draw in your paver project. You'll have to play around with your design a bit, so be sure to use pencil and keep your drawing neat. Your project will need to have adequate drainage if you want it to be safe and durable. You'll also want to make sure that it slopes away from your house and other structures. To ensure adequate drainage, you should have a slope of at least 1/8" per linear foot (1/4" slope per linear foot is often recommended).
Order your materials. You have a lot of choices in the pavers you use. Most are brick or concrete, but you can find a variety of sizes, shapes, and colors. Find a style that is to your liking and that fits your budget either online or at your local builders supply store.
In general, if your project area isn't too irregularly shaped, you can safely calculate how many pavers you need by simply measuring the square footage of the footprint and adding 5%. If your design has a lot of curves, get an extra 10% over your best square footage estimate.
You should order a bit extra because you'll almost certainly end up having to cut some of the pavers to get the right fit. The fancier your outline, the more pavers you'll have to cut.
Outline the project area. Use string or garden hose to outline your project. Drive stakes to hold the outline in place and use a triangle to make clean corners.
Scope your slope. To avoid water pooling on your pavers, you want your pavers to be slightly above the surface of the surrounding ground at all points. Thus, when planning the slope, begin with what will be the highest point. Typically, this is the point at the bottom of the front door or otherwise closest to the house.
Drive a stake at the high point, and mark the correct height where the pavers will meet the door or structure. Tie a string around the stake at that height.
Drive a stake (if there isn't already one) at the outer boundary of your project. This will be your lowest point. Attach a line level to your string and then tie the loose end of the string around the outer stake at the height at which the line level tells you the entire string is level. Now from that line move down the stake at least 1/8" per linear foot (e.g. if it is 8 feet from your front door to the outer edge of your patio, move down the stake 1"), and draw a new line. Move your string down to this line. String cross-lines down the length of the project to ensure you mark the correct depth across the entire project.
If your project area has a variety of slopes, or if your design is irregular, you'll need to repeat this process in several points. It is absolutely critical that you get the slope right, so the more stakes, the better.