An easy way to make your guitar pickups sound better is by moving them closer to the strings. This increases their output, which most people find to sound better. Another way is by switching out the magnets used in the pickups, as different magnets will give your pickups different tonal properties. This can only be done with pickups that use bar magnets, and can be tricky to do. Here's a guide from pickup manufacturer Seymour Duncan that can give you more info. A final way to improve the sound can be from changing the volume and tone pots on your guitar, which is a fairly straightforward process. Here's a link to a video showing how to do this.