Pete,
First, I recommend that you use roadbed under your track. If you have the roadbed on the correct alignment, then the track is a piece of cake. The roadbed will help your track look great. I use cork roadbed but others are fine.
Second, you will need a rail cutting tool to trim the inside rail on curves. When you bend the flex track, the inside rail will be shorter than the outside rail. A good tool like the one made by Xuron will cut the rail flush. It is important to get a good cut on the rail end.
Third, you should consider learning about wiring your layout for multi-train operation. The two dominant methods used for DC track (as in an HO train) are 'two rail wiring' and DCC. DCC has its advantages, but is the more expensive alternative. I use two rail wiring.
Finally, I layout curves using a combination of the 'distance-offset' method and a compass made from a yardstick. To make a compass, just drill a few holes into your yardstick at the correct curve radius. Then swing the yardstick around the arc and mark the centerline.
One thing I have learned is that you need to locate certain critical track elements first, like yard ladder tracks and the curves in the extreme corners of your layout.
If you have alot of space available, use broader curves. It will make the trains look better and contribute to better operation as well.
Good Luck - Ed