I agree with most of what's been said; like any other game, you have to work to be successful - you can't just leave the gam alone for three weeks, come back, and expect to have a pile of cash. You have to make strategic decisions based on what direction you want to take in this game.
My arena is almost 5600 cap., and sells out almost every game (except for a small rough patch where I lost a couple of games, I *do* sell out every game) - which is based on a combination of knowing what capacity you can handle, knowing how high you can charge your tickets, and performance on the field. The engine is built so that people will not pay too high for tickets if they feel they're being ripped off (and max price for a div IV team is definitely too high).
I also tend to scout 3 players a week - $40K/week is too much, IMO, and the difference between 3 and 4 is not that high in the end. And if I'm fairly high on the table after the all-star break, I'll often lower my scouting to 2 players/week.
I also agree that you don't need that many players. You really only need 13 players, IMO - one full roster plus one spare in case of injuries. The only reason I keep 16 is that I'm training several younger players ATM to sell later (which I can afford to do; if you want higher income, that's not an option).
Also, keep track of staff - often, staff at the same or higher levels pop up at cheaper salaries. It costs a full salary to get rid of the old one, but within a short time it will be worth it.
And look to the long term; I have to constantly remind myself not to be bothered by immediate results, as this game does not dish out instant gratification very often (I was unlucky enough to have a lot of success very early on, and now that it's tougher, it's sometimes hard to swallow). You have to be in for the long haul, or don't bother.
Like any good strategy game, it takes time to build your team in all of its regards - you have to play around with things to figure out what's best for you. The way I have things set up, I lose about $8k a week in a week with one home non-tv game, but I could easily be making quite a bit if I didn't have extra players being trained and lower staff and scouting - you have to decide your priorities, and take it from there.