This is what I personally did in my latest game:
1st Transfer Window:
In:
Jack Collinson - Cash + Stephen Ireland
Yann Sommer - £2.2m
Sime Vrsaljko - £2.5m
Ryan Shawcross - £14.5m (Over 48months)
Henrique Miranda - £925k
Andile Jali - £300k
Out:
Andy Marshall - Mutual Termination
James Collins - £3.0m
Stephen Ireland - P/X
Habib Beye - £600k
I've just started my second season now, I came 7th, 2 points off Arsenal in 5th and beat Chelsea in the League Cup Final. As you get towards the Jan transfer window keep an eye on Adam Johnson; whith the rate they buy players he often gets pushed down the pecking order and asks to leave. I got him for £4.5m and £30k p/w wages.
Yann Sommer isn't 100% nessecary tbh, but he is a quality keeper, only 22 and starts off better than Guzan (and is on less wages + Apperance fees) and is now (according to my staff at least) the best keeper in my squad.
Sime Vrsaljko is a fantastic right back and can go straight into your first team. Keep him around and he'll only get better

(And his wages aren't bad either, I think I got him on about £13-£15k p/w)
Ryan Shawcross I payed a little more than I would have liked, but he stepped up amazingly. Got fans player of the year, players league team of the season, came 3rd in overall MoM and scored me some vital goals (he put me 1-0 in the final and got the ball rolling.) I can not stress how great he was for me. Also he's young and British and as Cuellar and Dunne start to slip off towards the end of the season him and Clark are a great pair to build around
Henrique Miranda is a great prospect. He won't leap into your first team straight away, but train him up and play him in cup games and you'll have Man City, Man Utd, Bayern, AC Milan and a host of other teams hounding you for him by Jan.
Andile Jali. He is a quality DMC and a great replacement for Petrov who's legs have unfortuantly had it. Like Dunne and Cuellar Petrov seems to fall off towards the end of the season and Jali is a great prospect to build on.
Finally, Don't discount the players you've got at the club already: Bent got injured for 3/4 months which allowed Delfounso to become my top scorer with 17 Goals in 25 Starts (and 5 Subs). Gabby despite getting injured as well picked up 13Goals and 8Asts in all comps and finally my man Marc Albrighton (again) despirte getting injured for the last 5 months of the season picked up 15 assists in all competitions.
Villa have a good squad, but unfortuanly the wage bill is massive, once you get that under control it gets much easier. Good luck dude