Just use the flight sim for getting used to which way the needles go, practice tracking on the VOR, ADF, etc. It's very useful for that. Don't forget that things you are used to when visual have to be thought about when IFR - the tendency for the nose to go left in a single when you put the nose down, for example. Also remember that the instruments have a secondary function - if you haven't changed the power and your speed is increasing, you must be descending, hence the ASI is a secondary altimeter and vice versa (very useful for partial panel). And do not underestimate the humble VSI - it will tell you what's happening well before the altimeter does.