There are multiple methods for making a smooth track. If you want to build using only No Limits, then one tip is to only use ctrl+G when you have the segments ABOUT the right shape. For example, on an airtime hill, if you have only three vertices (start, top, and end) the autosmoother will probably produce bad results. Having more segments will get you better results from the autosmoother, but you will also have to position each vertex more precisely, and should try to keep each segment about the same length. For more information, you should ask a handbuilder.
The other main method of making smooth tracks is force-based designing, which these days is almost always done in a program called Newton 2. It allows you to create a mathematically defined element for insertion in a coaster (you can build an entire track as one element) by specifying initial position, speed and friction, then building based on banking and G-forces. Newton 2 allows you to build a smooth track fairly easily, but still must be tested periodically, as it is not perfect, and does not predict lateral Gs in seats not perfectly on the heartline (I.E. all of them). Getting manufacturer-accurate shaping in Newton 2 is also fairly difficult (trust me, I know).
Newton 2 can be downloaded at
http://coastercrazy.com/news/20/newton2
I won't tell you how to use Newton 2, since the creator has a good set of tutorials here:
http://www.youtube.com/user/TheRealEntropy
Hope this helps!
By the way, it seems like you're fairly new to No Limits, so I wouldn't recommend starting a big project right now. Get some practice by making a few simpler coasters, and when you do make your big project, it will be a much better quality ride.