I don't mean to sound harsh, but we really can't critique on this.
First of all, don't play level 9 CPUs. They make you worse, since bad habits like rolling to smash or that thing where you hit them up then starting charging a neutral B for a few seconds actually work. There's no way you could pull that off against a player that's at all good at the game. You CAN play level 1 CPUs, but ONLY to practice tech skill.
Second, the reason we can't critique you, again, is that stupid tactics work against computers. We have no idea how you would fare against a good person.
So, what's my advice?
1. Get your tech skill higher. You should be able to SHFFL with ease within a week or two. Same goes for wavedashing and dashdancing (second one should take about 5 minutes to master). All you need to do is figure HOW to do them, for this step. To find out about more (there are too many to list), read the Marth guide and, very importantly, the terms list in the main Melee section.
2. Watch the videos in the stickied thread on the Marth boards. These will teach you how to apply the advanced techniques. This will also help you learn things like spacing.
Good luck!