Not trying to be harsh on you Alex, sorry if I came in too heavy..I do remember my "beginners' blues" and there were things I did to plastic scale models back in my early years I should probably be prosecuted for..because I, like everyone, started off knowing nothing. Some think I still know nothing, but I digress...
You can see endless examples of good brush painting results in the photo galleries belonging to the various members here. Mine have some things you might find useful too, and I have some feature articles published here on my M16 halftrack build and a platoon of US soldiers to go with it. Lots of small stuff brush painted in all that.
Buy quality brushes. The best you can afford. Cheap brushes are usually polyester or other synthetic which is horrible for painting enamels on small smooth plastic parts. I use sable brushes and I like the results, but expect to spend $10 for one brush.
Paint tools definitely OFF the vehicle. Attach them after the painting is all done and completely dry, then touch up any little mishaps around the tools. If you glue them with plastic cement, use thin cement and scrape off the paint where the surfaces mate so it will fuse the plastic together. This isn't so vital with CA glues but I actually find it a stronger bond if I make that smooth plastic on plastic too, but you can glue to the painted vehicle with CA.
Use a magnifying glass if needed. No shame there. I paint radios with a microscope. Practice. Practice. Paint some leftover parts. Extra parts. Learn how to use the brush, how the paint behaves. Learn on pieces you don't care about messing up and you don't need. Practice. Keep thinner open and handy to keep the paint flowing right....STIR the paint very well, especially flats, these tend to separate and need re-stirring if you take a long painting session.
These are my best advice, my .02..Good sable brushes, and practice.