Double tracking is a tried-and-true method to make a single part sound bigger. Double tracked parts need to be fairly close in time with each other so that they don’t make the part sound sloppy. Yet it’s generally best if the two tracks sound slightly different; the differences makes the parts sound distinct and the overall result sound bigger.
This can be difficult if you’re performing a particularly difficult part that you can’t play accurately multiple times in a row. If you find yourself unable to duplicate a part, you can still double the part by splitting the signal at the source. You can split your signal using a dedicated splitter box, or using a stereo effects processor and send each output to different tracks. If you can, send each signal to their own, unique tone shaping path — send each output through a different amplifier, different stompboxes or processors, and so on. This way, you won’t need to play the part twice, while still gaining the advantage of two different tonalities. You can also duplicate the track you wish to double onto a new track, then process the new track by sliding it slightly in time forward or backward, running it through effects, or processing it with different EQ than the original track.