I found TechShopJim's great instructable here: https://www.instructables.com/id/100-Warp-Free-Make... about how to make an ABS slurry to help parts stick to the platform. This worked pretty well for me, but I had trouble with applying a thin layer and with storage of the slurry. This instructable details a similar technique that gives me a little better results with less effort, and an additional step to really help warp proof your printer.
Here is what you need to get started:
-Kapton tape (this method might also work with masking tape, but I haven't tried)
-Small squeeze bottle (http://www.mcmaster.com/#1902t14/=pmfznz)
-Scrap ABS part
-Optional: cardboard and tape for draft shield
Step 1: Fill Squeeze Bottle With Acetone
Step 2: Squirt a Small Puddle of Acetone on the Build Platform
Step 3: Rub Scrap ABS on Platform
While you are spreading the acetone, a small amount of the scrap part will be dissolving. This is what we are going for: to dissolve a small amount of the ABS part and deposit that as a thin layer on the build platform. You only need to spread this around in the area where you will be building your part.
Step 4: Preheat the Build Platform
Whatever the exact reason, preheating the platform really helps. I usually leave it on for about 10 minutes before I print.
Step 5: Print Part and Remove It From the Platform
Another option that helps reduce warp is interior part fill. The looser this is, the less risk of warping.
Finally, after the part has printed, it is time to remove from the platform. The parts usually stick so well after the acetone + ABS combo on the platform that this can be a challenge. I have good results with working an exacto knife blade under one corner of the part until it pops off. Another trick that helps is to let the platform fully cool down before part removal (but I usually don't have the patience!)
Step 6: BONUS ROUND: Make an Enclosure for Your Printer
I tried to approximate this heated build area by building a cardboard enclosure around my UP! printer. The temperature inside gets quite a bit hotter than the surrounding air, and it seems to help.