...I have to admit that my main problem with brushes seems to be letting paint dry inside the bristles of the brush. So I am trying harder to wash the brush more while painting and wash it at the end of a session with brush soap too.
When my (Rosemary) brush has come to the end of its painting life, I clean it with Humbrol Liquid Poly Plastic Glue - the stuff I use to stick hard plastic figures with.
DISCLAIMER - do this at your own risk...
I got the tip from Steve Dean's site.
Dip the brush in and leave for a minute, wipe with paper towel and all the dried up paint now comes out. Repeat until no more paint. Clean as normal. Use next painting session and, for me, lots more use.