Experience. Games can easily be won before you find any of your breakers. Rezzing ice costs money, and if they rez ice that just ends the run, you spent one click to make them spend credits and reveal what ice they had. This gives you time to draw up to either find the breaker you need, or tools to attack somewhere else. You also learn that against HB you should often run early in your turn, in case it’s clickable ice that you want to click through (the exception here is architect, an annoying sentry, though it’s better to have it fire once early in the game sometimes, especially if you can go check what it was used to get), against weyland you’ll often see barriers so you don’t care (caduceus is the annoying exception I’d say, and rare janus), and against jinteki, probably don’t run until you have some sort of sentry breaker, so you don’t hit komainu or cortex lock. Against NBN you can usually expect more ice that doesn’t punish you, like wraparound, unless you expect them to play a tag deck that tries to scorch you to death, so you need to expect gutenberg for example, which would give you a tag, meaning you need an extra click after the run to remove it. All comes down to experience
Corps usually don’t have the time and money to secure all servers they need to win the game early. So it means if you run HQ early and they rez Eli, you might just let it end the run, and then run on R&D to see the top card there. If they rez more ice and go broke you now have time to go find your tools, knowing they don’t have what they need to actually score agendas. Otherwise you might get to see what’s on top of R&D, if it is an agenda you steal it, if it is an operation you know they might play it, and if you know it is an ice, you now know what ice they might put down, and where, and what you need to break it.
Ultimately it comes down to practice, and experience. Just go watch some Andromeda stealth or Andromeda Datasucker decks from the last few years, or prepaid kate decks, to get an idea of how runners balance putting pressure on corps with developing their own boardstate, both in terms of economy and breakers
