Blaziken is level 69, and his move set is:
Hyper Beam
Double Kick
Fire Blast
Blaze Kick
Ugh. That bad moveset is exactly why you are not succeeding. First off, avoid two-turn moves like the plague. They are really bad. Avoid them. I mean it! Second, avoid using two attacking moves of the same type. That only occupies a slot that could make your Pokemon more effective. Lastly, get rid of Double Kick. It is worthless, when Blaziken can learn a MUCH better Fighting move. Here is what I would suggest:
Blaziken @ Leppa Berry
Trait: Blaze
EVs: 12 HP / 184 Atk / 60 SAtk / 252 Spd
Mild Nature (+SAtk, -Def)
- Flamethrower
- Focus Punch / Sky Uppercut
- Substitute
- Body Slam
The problem in-game Blaziken is that it cannot learn its best moveset until after you have completed the story and have battled in the Battle Frontier enough to earn enough BP to purchase Thunderpunch and Rock Slide. So, this moveset gives your Blaziken the best opportunity at dealing damage to the most types. First off, don't bother with Aerial Ace. You don't get STAB from it and the only type it is SE against is Fighting. Better to save that TM for a more worthy Pokemon. Also, go with Flamethrower over Fire Blast, Blaze Kick and Overheat. It provides consistent and 100% reliable power. You might need that extra firepower in competitive battling, but certainly not against the weak in-game AI. Substitute comes in very handy against the AI because it will randomly use a non-attack move, allowing your Sub to stick. Once up, you can then use Focus Punch to deliver a deadly blow. If you don't like that, then Sky Uppercut is a good alternative. I don't normally suggest Normal attacks on non-Normal Pokemon, but Blaziken's movepool is that limited. The added paralysis effect can REALLY come in handy.
Good luck.