I gather as much as I can in the 1st half of the board. Beyond that I try to take one of each group (to prevent other monopolies). I will usually auction off any 2nd or 3rd I land on in the grouping of the more expensive properties to extract more money for the properties from players, or if I have spare cash I may buy them and trade for something on the cheaper half of the board. Then I quckly build to at least 3 houses per monopoly (mortgaging others if necessary).Beyond that I prefer to stay away from the utilites, using them for little more than trade value. I also have the tendancy of using up all the houses and only building when I can re-use the houses on other properties preventing anyone else from building.
I know it sounds like a lot, but my family and I play Monopoly pretty frequently, and I don't lose very often.