Do you tend to tow the line between "now" and the "future"? One of the biggest weaknesses I see in keeper/dynasty leagues is people who try to cover both. I see many owners who are in the hunt in Aug/September but wonder why they fall short meanwhile they are say holding 2 roster spots for guys who wont be up for another 1-2 years or are carrying a young SP stud who will be shut down in September. If you are in the mix sometimes (4th as you say) and perhaps you dabble in youth too much I would suggest doing everything you can for right now. Be it:
Taking less youth vs veterans in the draft - in keeper formats youth is always overrated/overvalued. Many times you can get the same or better stats from that unsexy veteran. I see guys like Konerko be an undrafted FA in these formats just because everyone is piling up on kids. Thats an extreme example but it DID happen and many other veterans who can contribute end up being unwanted.
Trade any youth you can to make a run for it - same principle, you can get huge returns for great keeper players especially if you shop them around to everyone.
Trade down in the draft if applicable - theres bound to be some folks who want to trade up to get some youth so take 2 lesser picks for 1 higher and get more stats net. Or any other combo of trading.
Now on that note obviously if you arent sure you can win this year, say youre in the middle, you have to tow the line. certainly if youre doing terrible you have to blow it up and restock.
Maybe none of that applies to you (the whole now/later balance) and without knowing more the only other thing id suggest is dont be afraid of risk trading to go over the hump. Might be a deal out there that looks bad on paper but if it gives you what you need dont be afraid to be the butt of jokes if youre trading the bigger name.
"I'm the man with the ball. I'm the man who can throw it faster than F***. So that's why I'm better than anyone in the world." - Kenny Powers