I was having a ton of trouble with PLA. It never wanted to stick to my build platform when I started working with it. I started searching online for solutions and I found a few.
The two best solutions I found were to use either hairspray or ABS juice. The recommended brand of hairspray is Aquanet Super Ultra Hold. You’ll know your brand of hairspray is working well if it makes the build bed tacky after you apply it. Here is some more information about hairspray : http://www.thingiverse.com/thing:28787
The second best I found was to use ABS juice. ABS juice is a mixture of 9 parts acetone with 1 part ABS. Its not a problem if you add more ABS into the acetone, it’ll stay at the bottom and be mush. The acetone dissolves the ABS and stays in solution. When you apply that acetone it’ll leave a thin layer of ABS on the build platform for your material to stick to. It works, but the acetone will slowly eat away at your Kapton tape as you apply more and more. I’m not looking forward to replacing the Kapton tape, so I’ll stick with the hairspray.
Good luck with your PLA prints.