Okay folks what am I doing wrong?

Painting semi gloss on baseboards and window trim.  It starts sagging or dripping and I pull paint off trying to smooth it out.   I figure I should let it dry since its pulling the paint up and making an uneven, messy surface.
Am I loading my brush too heavy in the first coat?  Too thick?  Should I make two thinner coats?
I'm painting over Kilz primer.  

I'm not a painter......just trying to repaint a room.

If paint is dripping you have too much paint on your brush or roller.  Most paints, unless one coat label stuff, will take two coats to get a desired finish.

Thanks!  I was thinking I could cover it in one.   I painted one doorway with a thinner coat so I can check it later.

On the rough patches where I've messed it up I figure to let it dry well and sand it down.  Probably have to sand some of it down to the primer again.  

Appreciate the input.

Add some Flo-trol to it and don't apply it so heavy.  Use two coats and it will turn out really smooth.  The Flo-trol really makes the brush marks disappear.

Got it.  Thanks folks