Return to an Route that has trainers that have Pokemon near or are level 25 here are some examples: East and West of Mauville city or the Trick House.
This depends soley upon what type of training you want to do.
My personal favorite spot is in and around Mt Silver
the best Pokemon are on 1 2 and 3 islandsb
in the lilycove department store
the best place to train is on snover in snowypoint
You just have to keep on trying to catch it
there is no specific spot him and latias wander around hoenn
there is no best spot
victory road
Yes it is, you should start the quest with the mayor to gain access to the alien base. That is the best training spot for level 90-120.
The penalty spot.
Press the A button repeatedly near the spot the itemfinder is leading too.