Lookong at getting people's perspective on how they use margin on stocks. If you use the old saying of only risking 1% or 2% of your capital on any one trade, how do you end up using leverage. Say you have a 3% stop for example and that represents 1% of your capital. How can you leverage up if you want to keep the loss to 1% or account. Add to winners that are already in profit I guess could be a method. Or possible using extremely tight stops, but then win rate will be effected. So how do YOU use margin beyond your initial cash.
You will have to size less. If you use tighter stops than the setup demands, without regard to volatility or S/R, then you will constantly be harvesting losses without fully realizing the favorable move. You have been on ET since 2006 and you are only asking this now? This is the first question you should ask and figure out before your first day of live trading.
In general terms, you really can't until margin you use your initial cash. As long as your initial cash is still there, and available, then your broker will use it on any position you take. However, if you are day trading and use up all you initial cash before settlement date of previous trades then your broker generally will allow you to use margin to trade until the positions you exited from get settled and your settled cash is back in your account. Rinse and repeat. Ad naseum.
I try to use as little margin as I can to keep my broker happy. If he is happy, he doesn't ask me to take my business elsewhere and I get to keep other perks.