Basically, put a headband where you want your fade to start fading. Use whatever level you want the lowest to be at and shave off everything below the headband. Then take off the headband. That gives you a nice clean line where you use a higher guard and trim a little bit on that line. Just half to 1 cm. Switch the next larger guard and shave another half to 1 cm. Then repeat until done. Works best for mid to high taper fades and first timers. I did this starting out and eventually was able to make the line without a headband. I messed up my hair last week though. I was doing a little touch up and put the wrong guard on...
For the top, I like to keep my hair reasonable medium length of around 4"... which is more like 5-6" right now. I figure there's no point wasting hair product being inside all the time, so even though I swore I'll never grow out my hair again, my 2017 man bun is making a come back.