There’s no such thing as proactive tuning. Either you do it right before it goes into production (in which case it’s called “design”) or you react to the nasty surprises you get after it’s gone live.
Even if you do something about the problems before anyone has complained that’s still “reactive” not “proactive” – and the trick is to be reactive as soon as possible. For most companies the best strategy is probably to stick a big screen on the wall with the “Top Activity” page from OEM (or equivalent) so that the key players (DBAs and Developers) can keep a casual eye out for resource hogs and prioritise dealing with them as they appear.
Footnote: if you fall into that rare group of people who can look at what’s currently happening, identify the design errors, and explain how to fix them before the performance starts to nose-dive, then I’ll let you say you’re doing proactive tuning; but personally I tend to call that process “eliminating design errors”.