First, I am still very much a begginner, so take everything with a grain of salt.
I develop when my opponent is going 100%, because I must use technique.
For me, I think I develop my technique most when going against someone who is substantially stronger than me and not afraid to use it. When I am going against someone smaller, I can muscle through some techniques. When I am going with someone noticeably larger and stronger, evening surviving, much less getting a submission, is all about technique. Going against someone smaller, or someone who is not using their full strength, I might pull something off like an armbar because of raw weight overcoming their resistance. If I do it against someone larger and succeed, it is because of tight technique overcoming their strength.
I also frequently ask for feedback, especially when rolling with someone much more experienced (but even people less experienced can sometimes give good feedback).
(Just to be clear, when I say going 100%, I mean they aren't holding back, deliberately going light, or trying to be easy on me. If someone is actually putting in 100% muscle effort every single second and never relaxes, they may not be taking the best approach. The only time I've faced that is with people in their first week or two and they tend to tire themselves out very fast if they aren't amazingly athletic. In that case, you may be able to play defense until they wear themselves out, then focus on the technique you want.)
Consider flow rolling
Flow rolling is the idea of deliberately changing position often and both partners focusing on technique. It is discussed here: http://www.grapplearts.com/Blog/2012/07/5-ways-you-can-best-use-open-mat-in-bjj/ This is in a sense reframing your question since flow rolling relies on both partners agreeing not to 1go 100%. But when they agree it gives you a chance to practice techniques without worrying about strenght - yours or your partners. It also gives you both a chance to experience more positions in one bout since neither of you will try too hard to hold the top position.
Drill, with feedback
Again, it may be something of a dodge if you want to know how to practice technique while they are going 100%, but in the spirit of the question, if you want to improve a specific technique, drill it over and over with a partner who provides light resistance. Preferrably a partner who is experienced enough to give you specific feedback and tweaks.
Self impose limitations
I have never tried this, being a beginner. But some of my more advanced friends and some articles talk about imposing limits that make you rely not just on technique but on specific techniques. This doesn't require your partner to accept, or even know about, the limits. If you want to get better at armbars, call your shots before the opening bell. The only submission you will try is armbars. This helps you focus on the technique and the setup.