This is really basic for those of you who have been quilting for a while, but for newbies and self-taught quilters this is important.
You want to use Sharps for all your machine piecing. A good basic size would be about an 80/12.
This one I didn't know for quite a while, but you should change your needle after every good size project you work on. A needle gets dull and worn out after puncturing fabric a million times. If you hit a pin, it can get a burr on it. This can cause the needle to snag on your fabric each time it enters the fabric. Sometimes you can even hear it when a needle has gotten dull.
If you are having problems with the needle pushing the fabric down into the throat plate and making a mess, this could mean you have a dulled or burred needle and need to change it.