Listen to any good, modern recording, and you'll notice that the guitars and harmony vocals sound exceptionally lush and rich -- and that's most likely because they doubled the tracks. In very expansive multi-track productions, there could potentially be multiple layers making up those doubles, too -- it's all about creating as much space and depth as possible. In your home studio, though, one layer of doubling should be enough to see a huge difference.
There's two approaches to doubling, and you're welcome to try both of them to see if they offer you something you like. The ultimate goal is to create two tracks for one instrument, and pan each of them hard right and hard left -- with both tracks being different in some way.
First, the most common way to double a track is to simply record it two times in a row. This is a very easy way to do this, but it requires doing two good takes in a row. Don't worry about little variations on timing or feel -- that's what makes a good doubled take, anyway. Pan these tracks hard right and left, and you've got perfect doubling.
If getting another usable track take is going to be difficult, you can easily double a track from an already exiting one. Simply make a copy of the track, and pan each track left and right. Now, here's what it really takes to make the track a good double: you need to sample-delay one side of the track so that it ever-so-slightly nudges ahead or behind the other track. Without this, it'll sound as if it's one mono track without any variation whatsoever -- not the effect you want!
Using these two methods, it'll be very easy to double any tracks -- be it guitar, keyboards, or vocals.