I used to play as Ike, so here's my general input:
Ike is a punisher, he has limited options when it comes to offense or approaching, so the defensive game is your best bet. Simply avoid, mess with your opponent (this is technique that's applicable for ALL characters) and find an opponening- then punish. Punish hard. A single move will send your opponent a good distance, and put you in a good offensive position. Your opponent will likely be in the air, or falling towards the ground, which means that you can use an f-air and cancel it with the landing animation, then go back into a defensive stance if you happen to miss or they dodge. If you do hit, they're probably off the edge and you're in a position to meteor smash, and if that doesn't kill simply edgeguard as they attempt to recover. If you're invincibility frams have run out as they do their recovery attack, you can either fall down in a counter stance for the kill (risky as you need a fast recovery) or leap into the air and prepare to counter their stage return.
Generally your standard combo is your best tech-breaker, it's one of Ike's fastest moves (it's a very nice move for it) and the combo sends them into the air so you can begin your offense. A good approach is his side-b + normal combo, assuming you end the dash right before you reach your opponent. If you do that, you can actually link the end of the dash into your standard combo with little/no lag and begin your offense again. If they DI towards you, they're smashable, if they die away you can fair them. Either way your offense begins, but be prepared to leap into counter stance.
As an Ike player you should remember your sheer power and use it to your advantage, to prevent your opponent from returning to the stage. A hit off the edge with Ike is pretty much a stock. Remember though, that being off the edge is a huge risk/reward game for Ike, as his recovery is easily one of the worst, and you have to make sure you can make it back okay. I suggest his backwards-jumping and then using your back-air, it's his fastest move and easily one of the strongest, if one move is god it's Ike's back-air, and it gives him the time he needs to appropriately recover.
Now projectile users, they destroy Ike's defensive game entirely because you can't simply wait around now, you have to go on the offensive. So use your side-b to approach, remember to powershield any attacks that come your way mid-dash, and then go into either the standard a combo or do a backflip into a b-air. Either way the moves are fairly lagless so you can easily reach counter stance, except now you'll have a better position- close range- meaning they're more likely to initiate a melee assault (so you can return your defensive game). Now, if they attempt a retreat simply repeat the process, but the distance will undoubtedly be shorter and the projectile-lag they'll suffer will allow for an easy hit. Remember you can't always use these techniques simply because they become predictable, however they're probably your best options. Mix up your lagless moves, and focus primarily on punishing mistakes until they're vulnerable. They're most vulnerable after you've hit them, as you restrict their options and increase yours. Ike's nair is also a very good move if you want to use it (although never use it before a recovery, as there's a good chance you'll fall to your death during the animation) but it's laggy so land-cancel it.