What you want to do is try and stay at about a mid range, where ROB's tilts wont reach, and do some empty short hops, fox trots, SHADs, egg tosses (both aerial like another short hop and grounded), etc, just to mess with his spacing. Dont try camping from far away as that just allows his lasers to be safe and gives him free gyros. Stay up in an area where if he tries to do anything, you can punish with a DJC egg lay, a dash attack, a dash grab, etc, and just keep the pressure on. Dont be too aggressive, as ROBs ftilt, fair, grab, and dsmash will eat any attempt to force your way in, and just constantly apply pressure just outside of his immediate range. If he tries to charge gyro, drop in with a nair or egg lay to force him out. To stop lasers, weave around with your short hops and such to make yourself unpredictable, and if you see one coming, punish. Over time, if you can keep pressure on ROB, he'll start running out of options and will be a little more aggressive. Take advantage of this by trying to get him into the air, where your usmash will be a huge threat and you can punish landings.
When it comes to approaching ROB, you need to get him airborne or low on shield first with your camping game. If an egg connects, try to pressure his landing or get an egg lay in. Once you get him there, try to juggle him. ROB falls slowly and isnt too fast in the air, so just keep the pressure on. If the ROB likes landing with moves like Fair, bait it with things like pivot grabs. If he nairs/bairs, sliding egg toss. If he tries to Air Dodge, dash grabs, egg lays, etc. Just try to keep him in the air. Now, lets say you cant get an egg toss or egg lay too connect, then just try to wither down his shield. ROB has a pretty easy to poke shield, so when it starts getting low, try getting bairs on it, or landing with nairs > jab/tilt mixups. When ROBs shield hits about halfway, he has to tilt his shield just to stop your tilts, so an angled ftilt will shield poke, as will dtilt. And, to make it even more annoying, falling nair > turn around bair can be a great mixup on his shield too. Basically, just play a heavy poke mid range game and apply as much shield pressure as you can, and once you get in, get him up and try to stay in.
Now, what you CANT do, is try to camp full stage, that just WONT work. He'll start getting free gyros which control the stage and allow him great movement with glide toss and more keep away options. It will also allow him to laser freely, and will allow ROB to get comfortable and just be a pain. You also cant force an approach when ROB is in a neutral state. His ftilt and fair will wall your options too well, and you need to work him down first. Also, dont try to compete with ROB in the air, try to always be below him. If he's below you, be VERY careful and just try to get to the ground as safely as possible, ROB trades really well with Yoshi and most of the time it wont be a good trade for us. When it comes to killing ROB, dont force it. A simple knock up > read with uair, nair, or usmash can handle that, as will a landing bait with fsmash or a punish with bomb. Kills really arent too difficult on ROB once you have him where you want him, so dont get horny for blood.