Everyone is required to look at this thread. You could even comment on these tips.
Week 1
This is the most helpful tip I know. Put as many structure to track connections on your coaster as you can. But here's the tip, sometimes that's hard so try attaching a connector to the flexi, every connection doesn't have to go in the hole in the bottom for rods. Also, don't force the track into a connection. That deforms it and causes bumps. Another thing...You don't have to use the standard sized rods to make a connection either, you can make any kind of connection. Here's a great example of what I mean.
Don't stress over it, the hardest part about making these coasters is making connections, but the hardest part is finding the right combination out of the millions of possibilities.