Depends on how many trades you make, and lot sizes too. Personally, I'll never commit more than half of my equity to margin.
Say I have $10,000. That means no more than $5000 is on margin. Typically, it'd be even lower than that. Usually around $3000-$3500. The only time I'll go up to $5k is due to say a news release or something of the sort, where I can make a quick 15min-2hr trade. I like leaving a lot of equity aside for my positions. Having an abundance of equity to cover unrealized losses is always a good idea. Trading too much at once is what will really burn you.