I really recommend getting a strong handle on how the dual actions of horse and rider interact while mounted.
Basically the horse gets a full action, or move and standard each round and so does the rider. The rider tends to be limited on his actions depending on how the mount acts.
Mount double moves > Rider may melee attack once at the end of the move or beginning, may cast a spell (penalty from movement) or perform another standard action in between the mount's move actions, or perform a full attack with a missile weapon at the mid-point (penalty from movement). The rules were not clear on whether you could dismount and act after a double move, or act then mount and double move.
IMC: Personally I ruled that normal mounting and dismounting used up a move action from both the rider and mount which cleared a lot of the wierd combos my players tried the first night of riding combat. Quick mounting/dismount used no actions - however total movement was still restricted to a max of the best double move (or any combination of 2). And casting/missile combat whether mounted or quick mount/dismount still suffered the penalties for double movement.
Mount single moves > Mount may attack once with DC 10 for Rider to attack too, (IMC: since the Ride check mentions only attack I ruled that any other standard actions were not possible if the mount attacked). Under handle Animal it gives directing a trained animal as a move action so if the mount needs to attack in a certain way it uses up a rider's move action (DC 10 Handle animal to direct attack). If the mount doesn't attack then you can do a full missile attack before or after movement, a single melee attack before or after, cast without penalty before or after, or do another standard action without penalty - plus have a move action available.
Mount only 5' steps > Mount may attack with full attacks, DC 10 Ride for the rider to full attack also. Otherwise same actions as when a mount single moves.
Mount charges > One charge attack for mount and one charge attack for rider with the DC10 Ride check or skip the Ride check and just a charge attack for rider (may also take a move equivalent before attack). Unclear whether a mount could advance the needed 5' to attack after a lance attack at 10' was made - probably not except with Trample.
Mount charge with Ride-by > No attack for mount, one attack for Rider when in range. Note: by the RAW the mount would be required to do an overrun by the line of charge rules - since overrun cannot normally done as part of a charge (without Trample) it means Ride-by would be improbable as written. Suggest leeway in the line of charge so that continued movement would allow the mount to continue moving in line while still allowing an attack at the closest available space.
Overall review Ride, Handle Animal, and the Mounted Combat section. Pick a interpretation for how mount and rider actions resolve so you don't get into goofy situations where players try to mount, move twice, then dismount, move twice with mount and then once more, or try to avoid riding penalties for spell/missile by dismounting then remounting.
