As someone who is in the same process right now, I'll give you some basic suggestions.
Dash dancing, and by extension, CCing it into other things. Lucarios dash dancing is one of his strongest options, so you need to learn fundamental things around it. Learn the feel for how far before lucario stops dashing and starts running. Once you are running, you can crouch at any point to either attack or turn around with minimal lag. Cancelling lucarios dash with a crouch is a great option because it will allow you to dtilt or dsmash, or even restart your dash dance.
Try to start getting used to ASC. The first two things I would focus on are Dash attack>ASC and Fair>ASC. Trying to hit ASC's off of these moves should give you lots of practice opportunity, and once you can do them, you can put them else where in combos. Remember that you can light press and hold either shoulder button before inputting your nb and it will cancel right away, just make sure you dont depress the button early.
Lucario's kit is beautifully design to reward you for understanding his kit and using it to build combos around your opponents reactions. As such, you kind of want to know what each things does.
Also remember
Jab/DA--->tilts---->smashes--->specials
or Ariel--->specials
Here is a very shorthand
Jab and Dashattack are combo starters.
dtilt catches grabs, utilt hits behind you, ftilt steps you forward
Usmash is antiCC, Dsmash hits behind you, Fsmash is fsmashy
sideb beats shield, down b keeps you safe or crosses up
So its important to become familiar with your tools and build your combos based off your opponents reactions. Its kind of like throwing a puzzle at your enemy, and then changing it once they start to solve it.
I.E.
If your enemy is shielding > Dashattack >Dtilt>side B should grab them before they can do anything (shffled fair>sideb works well too)
If your enemy is crouch cancelling Dashattack >dtilt >Usmash >fair /nair
if you notice the dash attack send the enemy into the air behind you DA>utilt>dsmash
Down B can catch rolls, SideB can catch spot dodges with the damaging part
Lucario is very theory based, so be sure to dig around this section and do your homework and you will find lots of cool stuff.
As a PS, if you can moonwalk, lucario can make surprisingly fun and good usage out of it too.