Agreed - exceptional body control is paramount. A horse who will willingly guide wherever you direct him despite potentially new objects/strange colors/movements/smells is necessary because it's highly unlikely you'll be able to expose your horse to everything that you'll see in a pattern.
Smooth, precise gait transitions require no props for practice, but putting out a few cones (or buckets, chairs, fence posts, poop pile, using any sort of visual marker) gives you something to aim at for precise timing of changes.
As has been mentioned in other posts here (search for "trail class" or "show trail",) trail patterns today are often a mass of poles - practice walk/trot/lope over poles while maintaining your rhythm & cadence. Set up a box of 4 poles to practice traveling over at all gaits. Practice trotting into the box with a nice smooth halt & turnaround inside - your horse really needs to be listening to you to know whether he should continuing moving through the box or stop inside it; he may start anticipate once you have asked him to stop in it a time or two. Practice your sidepass over these poles, too.
Check your the rule book for whatever organization is hosting your show to determine appropriate attire. Boots, hat and long sleeve shirt is generally the minimum requirement, which is likely similar to your existing gaming attire. There are other show clothing posts here if you want to get a different outfit, of course! Splint boots/bell boots/leg protection are usually not allowed on your horse, and you'll need to verify your bit's legality - those are two things that could potentially differ from your gaming competitions. Have fun!