You really just need to do combos. I don't know what combos Ganon or Roy really have, but Lucas is usually very easy to combo due to his weight and fall speed. Your friend is probably also not very good, so your basic strategy should be to play patiently until he does an attack or tries to grab you and then punish him. If he does an aerial from far away you can shield grab him unless he has good spacing. You should also be using your dash dance and wavedash to bait attacks and avoid them, which will allow you to get punishes when he tries to do something and misses. One of the best things you can do is go into training and just practice combos on Lucas. Set him to attack (I'm not sure what the best level for DI is, but I usually just use 3 or 9; I think level 9s might be the best at teching, but I'm not sure), turn on the HUD so you can see the combo counter and then try to kill him with one combo where it counts all the hits. The HUD combo monitor checks whether the opponent is still in hitstun when you land each hit, meaning that if it counts all your hits as a combo then your opponent wouldn't have been able to attack or jump out of the stun the whole time. A good player might still be able to DI out of the combo, but different computers will do the correct DI at least sometimes, and even if they don't DI very well this is still the best place to start practicing your tech skill so that you don't mess up when you're playing a real match.