It takes some practice, but the main notes to remember is to make sure that your hills, curves and such are smooth (the smoothing tool helps, but a lot of it has to do with the way you plan it out also), and that your coaster maintains enough speed to make it through the next section (so make sure to test the coaster every now and then during construction to see how the train moves through the track).
Since the simulation aspect of it isn't in yet you don't have to worry about things like nausea and excitement ratings yet, so practice building all you want while you can.