Laser, and practice your post-laser options. Dash Dance forward or back, laser in place, approaching laser, sh aerial, etc. If you want to sh aerial, make sure to overshoot it, as almost any character will dash back. I think the default should be to overshoot aerials, but undershoot can be good too if they go for DD grab a lot. You should note if your overshoot connects to try to get a grip of how campy your opponent is willing to play.
Once your opponent is fully pushed into the corner, he has to pick an escape option. If it's Marth, common options are roll, shield, and FH fair. In this example, ALL of these options BEAT approaching nair. Instead, you can laser grab, undershoot sh nair, or dash dance around SH fair range. These are just some default options, but you can get cheekier as you get to know their options. If they stay in shield, double shine grab. If they jump, catch it with dair or nair. If they roll, shield pressure into turn around sh dair. Think about your opponent's habits and adjust accordingly. Every option can be beaten, so remember to use your brain.
More than anything, try to be patient. This is the most difficult point as it is far more abstract and involves tempering your mental. Try to dash dance further away and get an idea of what your opponent can do to you at various ranges. Think about what your opponent is capable of at X range, and lab what you are capable of at the same range. For example, one time I just labbed close laser -> max dash dance -> nair against a Marth nairing out of shield. Helped me a ton in the matchup.