Knots of the intentional type weaken nylon breaking strains by up to 50%. Other knots, such as wind knots and necking loops, weaken nylon by so much, that you must retie your leaders when they occur. There are only three or four knots to learn: nail / needle knot, 2 and 3 turn water knot, half-blood knot (perhaps tucked) and, optionally, the perfection loop.
Apart from the nail knot you should, with practice, be able to tie them in the dark. You might be wondering as to the practicality of this. Well, assuming you can make early starts, then it's dark. Also, very importantly, torches have two effects; the first is to scare fish, the second is to destroy your night vision. If you have to tie a fly in the dark and are having trouble locating the eye with the monofilament, then try placing the eye on the tip of your tongue and feel for it.
For double strength monofilament and copolymers make sure your water knots have three turns. Four turns can weaken them. Always pay great attention to your knots.
If your leader develops knots on its own initiative then replace it. Even kinks should mean a leader renewal. And always, always renew your leader with each outing.