Following this has generally given me good results.
http://www.fm-base.co.uk/forum/f72/woifsongs-teamtalk-guide-t29092.html
In short what it says is if you are favored, and there are reports of complacency, use "expect a win" as the general team talk with individual talks to the players that are reported as complacent of "expect a performance"
Then if you have a lead at half use "dont get complacent"
Playing as Chelsea myself I rarely have problems with the veterans (Terry, Lampard, Anelka, Drogba) but I have to get on Alex, Cole and Malouda at times plus a couple of the new additions.. Also if it gets to be a recurring problem with certain players, a couple of matches watching from the sidelines can help reinforce the point.
I'm in March in my first year and despite being 10 points clear in EPL I am seeing less and less reports of complacency.