Deciding on what type of tracks to use for your layout is one of the more difficult decisions to make when first starting out. There are pros and cons to each brand.
Atlas is probably the most commonly used track because it is generally much more available in local hobby shops than some of the other brands, although Bachmann and Lifelike brands are a close second and third, especially in HO scale or N scale.
Peco and Shinohara brands are favorites among many model railroaders since they appear a little more realistic than the others and they have curved turnouts available which many of the other brands do not.
Kato is excellent for N scale, easy to assemble and is very reliable - less problems with derailments. Kato in HO scale is also available but a little harder to find. Bachmann EZ Track and Atlas Try Track are also easy to put together, includes the roadbed with the track and are also very reliable for HO or N scale. Unfortunately, there is no flextrack for these easy-connect, roadbed-included tracks.
I personally like to use flextrack whenever I can because many times the standard sectional track just won't fit where you want it to go, plus it has fewer joints which usually translates to fewer derailments.
Try to keep the track code (referring to the vertical height of the rail) the same throughout for your mainline. Code 100 is what I like to use. Branchlines tend to be a little smaller, like code 83, but if you're connecting code 100 with code 83, you will have to use an extra thickness of roadbed under the branchline (code 83) so the tops of the rails coincide where they meet.
The best turnouts to use even on small layouts are the #6 turnouts. #4 turnouts are too short, less realistic and cause more derailments. #8 turnouts take up too much space and are usually not necessary.
Straight parallel tracks should be at least 2 inches apart. Curved parallel tracks should be at least 2 and 3/8 inches apart to avoid railcars side-swiping each other.
Curved track should have a radius of no less than 18 inches usually unless you are laying track in a very mountainous area using short locos and railcars. 22-inch-radius curves are usually more realistic and cause fewer derailments.
Remember to have a balance on your layout of scenery, tracks and structures. About a third of your space for each.
Don't put tracks any closer than 2-3 inches from your backdrop so there is room for scenery and/or a relief of a building. Also don't put tracks any closer than 2 inches from the edge of your layout or you will be picking up the pieces of your $300.00 locomotives from the floor.