I try to lock up players that trend up sooner and wait on players that trend down. I also go 75% bonus and look to keep the overall dollar amount lower. It makes for a lot of dead cap when u cut or trade a guy but it helps with the overall cap room. I honestly don't know if it affects a players growth when give it him a heavily guaranteed contract or a higher salary with less bonus money.
On more way to get some room with older guys is to pay him low the first couple years and REAL high the last couple. You will have to cut him after two but gives you immediate room.
I had an old CB that I wanted to extend. Paid him like 1 million base first two years of a 4 year extension. 1.5 million bonus for 4 years and a base salary of 12 million in year 3 and a bit more in year 4. This was a way to get two more years out of him and created 1.5 of dead space in year
3 and 4 when he retired in year 2/3 of that contract. (Was gonna cut him anyways)
Hope this helps :)