How can you level your fighter up easly?

There's no truly easy way, but here's the quickest way I know.
Get a team of really killer dinos together. If your fighter is at a low level, leave off most of the superevolvers for right now, as they cost more FP, which is what you lack as a lower level fighter. Try to make sure it's a team that shines so you can use team skills. To get your fighter up to lvl 20, you have to do all the side missions, beat the game, collect all the vivosaurs (including duplicates of the ones that superevolve and superevolve them). After you beat the game, start fighting the main characters, not just the guys you run into around the dig sites. Todd is on the Fossil Lawn on Ribular, Pauleen is in the Hare Club on Cranial, Rupert is on the walkway in front of the Fossil Station on Ilium. Joe is in his office on Cranial. The BB brigade is also available. Lola is near the cleaning emporium on Ribular, Lester is in the shop on Cranial and Cole is near the entrance to Icegrip on Ilium. You can also go to Zongazonga's castle and pay gold to rebattle him or you can go to the museum on Cranial (after you've beaten the game, of course) and talk to the professor. He'll ask you to tell him about your battle with Zongazonga,which means you'll refight the zombisaurs and then Zongazonga and the Z-Rexes, for which you get 50 points instead of the 60 you get at the castle,but hey! It's free!
Hope this gives you some ideas. Good luck!

You can battle everyone or do side quests. Battle zongazonga. P.s. If you don't know already DON'T TRUST JOE WILDWEST!!!!!!!!!!!!!!!!!!!!!!!!!!!

Is Level 20 230 FP Recharge and 900 FP Max?

The way I level vivosaurs up is really fast, but gets very boring. You can get a team of Raja (AZ Front), Tricera (SZ Left), and Sungari (SZ Right). Use Raja's Charge and Tricera's Enflame on Raja. Then unleash Raja's Team Skill to fend off the others. This works best with Todd's Team.

The pst game is really hard and the only way to level up your character is to do all the side quests and beat the main characters. They are cool and hard to beat. There is Todd and Lola in Ribular island. Pauleen and Lester are on Carnial island and so is Joe Wildwest but you fight him in the BB base for the ultimate tournament. Rupert and Cole are on Ilium island. I wasnt sure if you didnt notice but there is also the dog princess in one of the guilds on the islands but I forgot which one. And there is ZongaZongas palace and the last one to be Robbie or whatever his name was he was in Bonehemoth.