Obvious way to get an experience level advantage?

Getting a level advantage of 3 levels or more?

Kill your lane opponent. Then do it again. And again. Pretty obvious, as your title asks. Probably easier with the jungler camping you.

Also helps to zone them out of creep xp range once you've got a 1-2 level lead and some gold lead. Also helps to do jungle camps (preferably the enemy junglers) whenever your lane opponent recalls.

Otherwise, no - I don't think there's any way you can reliably get even a 2 level lead against someone who's playing at a similar skill level to you (even if you only care about optimizing experience gain and give up anything and everything else to do so). You need to get pretty fed to clear waves and jungle camps quickly enough to establish that sort of a lead.

Start with TP and take a jungle camp at lvl 1 the. tP to lane after recall

Run exp runes

After killing your lane opponent push wave to tower, go kill a jungle monster, return to lane

If losing lane push wave hard (depends on champions in game) roam to another lane and soak some exp (by mobi boots if you are going to do this)

Ward enemy jungle, collapse on him with team the. Take his jungle camps after he is dead

The most important aspect though is use and upgrade your trinket, vision makes doing a lot of these MUcH safer and easier

Constantly take the small raptors.... its 80 xp up every time you do it. it can really benefit you.