You can boost the level of your monsters and then use Transmodify to special summon from your deck an even higher stronger monster, You can also use the skill monstermorph: Evolution for the same results. With Advance Force you can tribute summon a level 7 or higher monster with a 1 level 5 or higher monster as tribute.
Beatdown! (skill) This turn, the ATK of all face-up monsters on your field increases by the number of monsters of Level 5 or higher on your field times 300. This skill can only be used once per turn
Monstermorph: Evolution (Skill) Can be used each time your Life Points decrease by 1500. Once per turn, send 1 Monster on your side of the field (except a Token) to summon 1 random Monster (that can be Normal Summoned) from your deck whose attribute and type are same to and level is 1 higher than the tributed monster.