Kirby lacks a lot of speed when mobility is concerned. Horizontal mobility is his glaring weakness. What Kirby lacks in horizontal aptitude, he makes up for in the vertical department. Being able to 'hover' with his jumps above and out of an opponents range gives him a strong bait game; especially when you're hovering back and forth over your opponent, and switching the way you're facing (which gives you different options). I'll elaborate more in a sec, but I feel I should also point out that Kirby has faster horizontal mobility when he's moving backwards for whatever reason. I'm not sure how much faster, and honestly the only place it's noticeable is when he is standing, ShortHops Backwards (torwards the opponent), AirDodges, and DI's back to where he was originally standing. It's a good bait, and it's good for convincing your opponent to come to you. Alternatively it can be used to poke at your opponents range without throwing out an attack; exposing yourself to an attack.
Back to my original point.
If you're hovering in front of a person facing them, they have their Forward tactics, and you have your Forward tactics. Kirby's range to, but are not limited to, and include the ShortHop and FastFall versions: ForwardAir, UpAir, DownAir, and RARBackAir, as well as AD into your opponent>UTilt, another jump, drop down and grab, and jumping past your opponent.
The options that I use in the face-to-face, Kirby aerial situation, position is SHDAir if I think the opponent is going to jump up (SHing it means I don't have to worry about landing lag or having to land at all), I'll jump again if the opponent is throwing out an attack (or if I get too close before I'm ready to attack or punish), or I'll jump past them if I feel uncomfortable or simply to get into my favorite situation, where I have my back to the opponent, (also good simply as a mixup). This position is versatile so lastly, I'd like to say that while this is not the position I generally use as an approach (face-to-face) it's effective when I'm pressing an advantage.
If you're hovering in front a person facing AWAY from them, they have their Forward tactics, and your have your Back tactics. Options: BAir (reg, SH, FF), UAir, as well as AD into your opponent>grab, another jump, or jumping past your opponent. While there may be less options, I find this is my favorite scenario as I believe it's Kirby's strongest. BAir is my go-to option. I'll retreatBAir, SHBAir, FFBAir, BAir in place, mixing up when and how I throw it out in order to stay relatively safe while using one of Kirby's best moves. Sometimes I fall close the ground> SHBAir to bait someone out of their shield. Mostly I hover in this position 'til my opponent attacks with something I can punish with BAir (which happens a lot). Once I open them up, if they go aerial after my BAir, I continue to hover/press forward with BAir, or if they land I land with them and read them. Aside from BAiring, UAir can be used as a mix-up approach though you have to time it where the end of the UAir is what hits since you're facing away.
When your opponent's back is to you, let's say because you jumped over him, he's limited to his Back options which may or may not be advantageous to you. If you find yourself against an opponent who has poor Back options, this may be a position you want to force regularly during the match. Their options don't necessarily even have to be bad as long as they won't beat Kirby's BAir in speed or priority. Generally you want your back facing them as well when you force this position, so you'll want to change the direction you're facing to fit this if necessary.
I know this is a lot of information, and yet, this is only one part of Kirby.
If you're going to be on the ground you'll want to stay mobile; not necessarily attacking. SHAD in and back out of an opponent's range, dashing towards and back and throwing out pivot grabs will help your Kirby ground game, but being effective in the air will do wonders for your Kirby while minimizing Kirby's lack of horizontal mobility.