For now. Not forever
- Know Your Character's Limits - Recovery Limits and Dash Dancing Limits as well as attacks and stuff.
- DI and Crouch Canceling- Staying Alive
- Proper Ledge Guarding - Finishing off kills and getting gimps
- Short Hop - THIS IS AN ABSOLUTE MUST.
- L-Canceling - Faster Combos, allows you to continue combos, and minimizes the time that you can be punished.
- Teching and Wall Teching - Knowing how is important. However this is where Smashers become predicable. Mix up your Teching and it wont happen to often. It will keep you from getting combo'ed if your not read and it keeps you alive if your are hit horizontally into the ground.
- Fast Falling - Probably the Easiest thing on the list. But know when to do it is the important part.
- Matchups - Very important. Most of the time different approaches must be used on different characters. Some combos work on some characters and some on others.
- Wavedashing, Wave Landing, Out of Shield Wavedashing, and Wavedashing from the Ledge - Very Important. Improves mobility by a lot and gives you new approaches.
- SHFFLing - Combination of Short Hopping, Fast Falling, and L-Canceling. Useful for most characters.
- Shield Grabbing - Shield Grabbing will decimate n00bs and it is a good punish for overused SHFFLing.
- Dash Dancing - MINDGAMES SON!!! The King of Smash got by with this technique for a while before he learned DI. Of course this was before he was the King of Smash.
- Dash Canceling - Underrated technique but EXTREMELY USEFUL.
- Jump Cancel Shield - It's like L-Canceling but for grabs. It shortens Running Grab time.
- Meteor Canceling - Keeps you alive. Does not always work against an opponent who expects it.
- Out of Shield Up Smash and Up B - Situational, not super important.
- Pivot - Not that improtaint if you know how to Dash Cancel really well.
In that order.
What character are you using so I can give you more specific information?
I will add more when it comes into my head.
Roy has a really good Dash Dance and a good Wavedash.
I recommend learning both.
Crouch Canceling Counter (Down Tilt after a Crouch Cancel) is Roy's best friend. However don't depend on it at high percents.
I don't know a lot about Roy's Metagame other than stay on the ground but here is an in depth guide