I recommend buying high quality brushes. While good brushes alone will not make you an expert, poor brushes will hinder you. For miniature painting high quality Kolinsky Sable Brushes like the Winsor and Newton Series 7 line are a good choice. Kolinsky brushes are known for their paint holding ability and fine points. The W&N series seven line is available in regular and miniature. The miniature line has shorter tips like spotters. Besides W&N I have Kolinsky brushes from Scharf, DaVinci, Kalish, Vallejo, Isabay, Raphael, Kolonok, Weber, Goldmark, Reaper Master Series and Rekab. The DaVinci Restauro and Scharff (made by Raphael?) are my favorite brushes. With their great points and paint holding ability only a few sizes of Kolinsky brushes are needed for miniature painting. A 3/O , O, 1 and 2 will do most of what you need. Add a flat or two and you should have all the bases covered.

It's a good idea to have a separate set of brushes for use with metallic paints. Even with a rigorous cleaning regimen it is sometimes difficult to get all the metal particles out of a brush. Golden Taklon synthetic brushes are a good alternative to Kolinskys for working with metallics, basecoating and drybrushing. Of course I never drybrush anything but just in case.

If you are going to invest in quality brushes you may want to get some brush soap like "The Masters Brush Cleaner and Preserver" or Pink brush soap. These are formulated for brushes and replenish some of the natural emollients lost in cleaning. In addition try a little hair conditioner once a week or so to restore brushes to original condition. Winsor and Newton Brush Cleaner and Restorer is great for treating brushes that have paint caked in the ferrule or are otherwise in bad shape. I've only had to use it once or twelve times but it really works. Be careful not to get any on the brush handle since it will eat away at the paint there as well. It will even strip minis.
The brushes pictured above and left are all 2/0 sizes even though they look different from each other. Top to bottom; Isabey, WN 7 Mini, Vallejo and Kalish. Note the short hair on the WN 7. It's from the miniature line. The regular 7 Series 2/0 is like the bottom brush in hair length.
From the top down; Vallejo #2, Scharff #1, WN 7, Rekab, Kalish all #0.
 Handprints Brush info
Bruce MacEvoy has a very thorough section about brushes on his site Handprint.