Always look where you want to go.
Don't look at your horse, don't look at the pole/barrel/ground, look where you want to go.
Talk to your horse. Have a good verbal cue to go along with your physical ones, it will help you (and your horse) to focus and remember what you are supposed to be doing.
Most importantly, relax and have fun! Even if you blow it completely, everybody's done the same thing (likely more than once) and nobody thinks less of you for blowing a turn or knocking something over.