I think this topic is likely too broad... we already have the Q&A thread, the match up thread, the mind games thread, the neutral game thread...
It's such a broad question that I don't really know how to answer. I'd probably suggest, "look up ESAM's Pika guide, read up on the Pika neutral, watch some Pika vids, and practice edge guarding and utilizing Quick Attack," and then come back with something more specific to ask, such as, "what can I get off of a ledge trump," or "what are some sick mix-ups into jab-lock Fsmash?"
If you're looking for miscellaneous little tricks and gimmicks to try, here are some things to chew on:
- Retreating SH Fair AC
- SH Dair (1) AC
- Grab release into Fsmash (dumb)
- Corner Grab release into run-off Bair
- Ledge trump into FF DJ Thunder
- Perfect Pivot retreating Ftilt and Fsmash
- FF Fair on shield out of grab range
- Thunder to interrupt strings
Otherwise, feel free to peruse the other threads. The thing about Pika is that he's a fluid character who doesn't have a simple and exploitable strategy, so the best you can do is improve your Pikachu vocabulary and match up knowledge.