I only have a few pieces of advice for any bus traveler in Thailand.
1. Carry your passport in your bag with you on the bus. The buses are stopped and the police will check your passport. It is better to have it out and open to your photo. You are far less likely to be hassled if you are proactive and polite.
2. Buses do not usually have bathrooms. Plan accordingly.
3. Carry toilet paper and some soap. The bathrooms at the way-stations do not have these luxuries.
Other than that, have a safe and fun time busing up and down Thailand!