Ok, my only tips from my hours upon hours of riding are as follows:
-Relax. Be loose, don’t hold on too tightly, simply use the handlebars for resting your hands or forearms.
-Tense up your legs when the attendant comes by to check your restraint. When you’re sitting in the station, the lap bar or OTSR should not be touching you, but should be very close. This still keeps you safe while allowing you plenty of room to stay comfortable.
-I’ve found that the front of the train will not knock you around as much as the back.
-For wooden coasters, try not to sit in a seat that sits right above a wheel. This really only applies to PTC trains that have 3 rows of seats per car. (Sit in the middle two seats)
Keep in mind; these are just general suggestions that will work on just about any B&M or Schwarzkophf coaster. You will need to adapt accordingly to different manufacturers, coaster styles, construction types, layouts, ect.