I am typing this assuming you havent signed anyone/sold anyone already.
GK - Lee is very good, wait until
Prem to sign someone else. Poom and Loach can be back up, but Lee is the best from the three of them.
DR - Mariappa will get alot of interest, try o sell for about £1.5mil if you need to sell, Doyley is good back up if you can keep hold of Mariappa
DL - Joe Mattock from leicester, when i signed him i sold him to Liverpool for £5mil + Danny Guthrie 2nd season, and he only cost £600k. If that fails, try to sign Watfords new LB, Mat Sadler, hes good eough to get you promoted. Jordan Stewart is another who gets alot ofinterest, so attempt to sell for £2mil. Jordan Parkes can provide good cover, but isnt going to be good enough for regular Championship football.
DC - Danny Shittu and Jay DeMerti are 2 of the best Championship centre backs in the game, but Matt Jackson is much too slow. Sign someone wither transfer/loan listed as back up, or to challenge for a first team slot. I reccommend jonny Evans from Man Utd. Players like Mahon, Mariappa, and Doyley can also play CB, so not much is needed.
MR - Tommy Smith is great, but more cover is needed. Keiran Lee can play D RL, M RLC, so he is a very good addition to any squad. Clubs like Derby will start offering prices up to 6mil for him if you get promoted.Chris Eagles on loan from man Utd is very good, he scores goals and sets them up!
ML - Jobi McAnuff is a good winger, loan Lee Martin from man Utd to provide back up and a callenge. Mika Aaritalo lays on the right left or as striker, and only costs abour 250k, soid get him BUT ONLY IF YOU HAVENT DOWNLOADED THE PATCH
MC - Watfords best position, Francis, Bangura, O'Toole, Rinaldi, Mahon, Williams, and Williamson are all capable of playing first team. No additions needed.
ST - Marlon King is arguably the leagues best player, hence he has now gone to Wigan. But he, Henderson, and Ellington, along with Priskin and kabba as back up, provides you with perhaps the best attack in the league. Id sell Kabba, and buy Zarate for about £2.8mil in Jan, he wont want to come in the summer
Watfords squad is one easily capable of getting promoted, without too much transfer business. Players from Man Utds reserves are normally avalible on loan, and the players from there normally want to go to you.
Hope this helps