Cutting Your Own Beard??? Read This
If you're going to trim your own beard at home and its past stubble and now really into "beard" length then your first point of call should be to make sure you blow dry it to smooth out any kinks that might be in there and to smooth out all the tightly curled hairs that are underneath your chin that will often get forgotten.
To do this use your hairdryer on a low speed and low heat and a small round brush that enables you to get the brush all the way or as close to the root as possible. Once there you need to start rotating down and out and with as much tension as possible to straighten the hairs as much as possible.
If you do this then you're in the best possible starting position for trimming your beard, it means you can see it in its most balanced state and can hopefully see where all the imperfections are.