Um.... yeah Lucas is hard AF to do well with. His inputs have to be precise and his playstyle is that of a perfectionist if I say so myself. Yeah you can get away with certain PKF and a few tech mistakes, but overall the character takes a lot of work. He's very rewarding however, as one punish can lead to very high %, ledge guards, and even stock kills.
I've been practicing him on and off since February 2014, don't feel bad if you aren't consistent or the best at him yet. The more I progress, the more I share with you guys to make it easier to get better in a faster, efficient manner.
==
1. B reverse / wavebounce / B turnaround
https://youtube.com/watch?v=R3UbHAq4Tk0#t=44m12s
This video describes the tech at the end really well. I time stamped the part that directly helps answer your question.
It's where I found out a lot of stuff that drastically improved my gameplay and further advances my knowledge of PM. Check out the full video if you want to, it's definitely worth 50mins of your time (and I don't say that lightly).
==
I wrote a post about shield pressure somewhere, but can't recall exactly where. Essentially there are a few methods and all of these are the best to practice with in my highly educated opinion.
The fastest to setup would be the starman method I list at the bottom, the one that allows you to continuously practice uninterrupted would be the first method, using a Bowser dummy. You barely have to reset the situation until Bowser is over 300% as opposed to constantly refreshing walls, shields, or items.
This may include wiimotes (haven't tested yet), nunchucks, GameCube controllers, and whatever other variation you can think of that has an analog input for Smash.
Standard versus mode
1. Select Lucas (or any character you want to practice) and set the CPU to Bowser
2. Turn damage ratio to 0.5x and game mode to Timer. Feel free to set the timer to whatever you want here. Timer mode allows you to kill off Bowser and not have to reset the game due to running out of stocks / time.
3. Plug in the controller holding Up on the analog stick
4. Select the stage. There are two options: have your random stage select
only on the stage(s) you want, or hold up on the 2nd controller then select stage with the 1st controller.
* I personally like Final Destination to practice on. You can move Bowser around freely with throws and platforms won't interfere at all.
5. Have fun practicing!
* Variation w/ 2nd controller:
Training mode:
Do the same process only now you select training mode with a crouching Bowser / Yoshi.
Have some way to press shield on the 2nd controller. Whether it be a friend, your feet, or a device.
You can't change damage ratio, but pausing resets damage to 0 and you can change game speed to 2x in order to refresh the shield.
Yoshi's shield never gets shield stabbed which is perfect to practice on. If the shield breaks, simply jab him and their shield will begin replenishing.
Training mode:
Easiest to setup: Shadow Moses Island.
Practice on the walls and use the 2x to make them regenerate if they break.
Still practical: FD + standing still CPU character
Use the Mario Bros. Star powerup item under the pause menu. Hit lag works the same. The CPU will never mode anywhere and it's easy to repeat. Best for practicing on any character size.