Hey Buddy, heres a few things I think Lucario excels at.
1. Air game
His Fair, Upair and Dair has very good priority and often you can pull off a few fairs at low %
His Bair is a kill move and Nair has low landing lag
2. Juggle proof
He has several methods to not get air juggled, a good B-reverse with hitbox, his counter, his dair stops him midair and his up-b if you can sweetspot the floor/ledge
3. Combo's
Although i'm not aware of many combo's for Lucario, Uptilt, Downtilt and Fair are excellent combo starters and at certain % you can fair into side b.
4. High %
Campy play when at high percent is fine, but I would keep that for your last stock, if you got extra stocks, I'd play agressive with a tad of zoning to maximize pressure/damage. Keep your fully charged B and use it to edgeguard or to hit grounded opponents who didn't tech to punish for big damage. It dosen't matter if you hit or not with side-b, use it from time to time to tell your opponent you got stage control, don't forget you can use it in the air or for edgeguarding!
You can break your momentum by using Dair, and if you master Upairs hurtbox and travel distance, you can use that as well to zone. Grab side B is a killmove and I believe Dash attack as well.
5. Low %
Not much you can do for damage, combo's will be your best bet, try mastering a few true combo's
I believe Grabbed side-B can be comboed from single jab or fair.
Grabs into combos will be one of the best ways to get dmg at 0%.
Hope this helps.