If you have a dual extrusion system, make sure the two extrusion nozzles are exactly the same height when you first install them. You may need to tighten screws or insert pieces of paper to do so.
When you first adjust the build platform, take your time. Getting the
platform the right height and levelled is vital to getting a good print. Too high and the extruder nozzles will scrape the tape. Too low and the extruded plastic wont stick.
Re-level the build platform at least weekly to make sure it remains in the best possible position.
Clean the Kapton tape between prints to help with print adhesion. You should clean it with acetone, or in a pinch you can use nail polish remover.
When the Kapton tape on the platform looks like it’s ready to be
replaced, it’s very easy to do so if you use the squeegee that came in
the box. Peel off all the old tape, then unroll the new tape a strip at a time. You can lift up the tape and squeegee it down several times if
needs be to get rid of air bubbles. Just keep it taut as you unroll it
onto the platform.
Heat the build platform to at least 110 degrees celsius, possibly 115 or 120. This will help prevent curling of edges.
Don’t be tempted to try rafts with dual extrusion. There is no way that will end well, no matter how carefully you set up the model. See above.
And if you do have a problem, the MakerBot mailing list, the MakerBot forums, and MakerBot tech support are the most amazingly helpful community I’ve encountered in a long time.