Probably repeat some of what been said but a better quality brush is important. When I first started in the hobby I bought really expensive brushes (Winsor & Newton Series 7 Kolinsky Sable Brushes) and honestly the only thing that I learned from them was brush care is important. I used to destroy my other brushes, the expensive ones I took care off. I recently been using standard brushes you can get at Michael's or an art store in the 7-9 dollar range with synthetic bristles, but the brush care stuck.
I've had good luck with these, but I tend to buy them in store to make sure they aren't damaged or have bent bristles.
https://www.michaels.com/golden-taklon-short-handle-round-brush-by-artists-loft-vienna/10011028.html
Rinse often, clean your brush and make sure it has a great tip. If you can, multiple sized brushes help but I've been using my size 2/4 for most of my work.
Paints - this will be somewhat of an investment. I use Vallejo and
GW brand paints. I like the
GW brand because they are easy to get in my area.
Practice / new techniques - washes and dry-brushing can get your model 95% there for table top quality+. Find some good youtube videos on both and practice.
These are two terminators I've painted one was a while back and one was recent.
Terminator 1 - primed with a rattle can, washed with a wash and applied some paint where I thought he needed it.
Terminator 2
- Prime with airbrush / can be done with a rattle can
- Zenithal primer applied with airbrush / can be done with a rattle can or a heavy dry-brush.
- Base layer of green with airbrush
- Block in areas with black that need it. most metallic paints go over a dark color better (notice terminator 1 has green paint showing through both the gold silver)
- Dry-brush the claws to give them a bit of power weapon look
- Edge highlight the green panels. This might be doable with a dry-brush but it's one of the areas where I want to improve so I try it where I can.
- apply wash strategically, in this case the wash only went to the legs where the different plates meet.
- edge highlight the shoulder pads