Homebrew PCBs

I've read a million post on the net about how to create a pcb with 
photosensative spray, and UV light and after about 30 failed attempts 
I'm almost ready to give up.

If someone could please check my method and advise me where I'm going 
wrong:

1) Clean pcb - this is not a problem as its really shiny afterwards 
with no oil on etc
2) Spray with photoresist. I've tried various thicknesses from almost 
see through to a nice clear purple film on the board. Left it to dry 
for 24 hrs. 
3) Created a artwork on tracing paper  (90 gsm) with a deskjet 
printer. 
4) expose using uv lamps - ive  tried various exposure times. 4 mins 
seems to give the best results. 
5) My caustic soda solution is 3 teaspoons to 1.5L water. Again this 
is from trial and error and sometimes seems to give the best results. 

From the 30 attempts I've had - one board was almost usable. The 
problem is that nothing seems consistent. One day I'll create a pcb 
and all of the photo resist gets removed in the CS, the next day with 
the same quantities, the outsides of the board gets removed - the 
purple photo resist film toward the middle of the board refuses to
get 
removed. I've even tried rotating the board under the UV light. 

Help!! Does everyone else have hassles like this? Is there any method 
I can use to produce good pcb's every time.