I've found that bringing in players that already play in England and/or speak the language is good for team morale etc as they don't have to spend time settling in and such.
Peter Pawlett was my best signing of last season playing as Brighton, averaged 7.49 at RM and chipped in with a load of goals and assists, winning Player of the Season and Signing of the Season in the process. Signed for around £800k from Aberdeen. Could also be worth looking at his teammate at Aberdeen, Cammy Smith, who has great potential and comes cheap.
I've found CM to be an awkward position to fill in the Championship but Oliver Norwood was superb for me last season. Signed from Reading for around £2 million, he takes a decent set piece, chips in with a few goals and is pretty versatile with roles.
Rico Henry is also looking to be a good investment as well. Signs for a few hundred k from Walsall, 5 star potential and improving constantly. Should be adequate for backup at LB in the Championship after a season out on loan.