There are two approaches I use for this. The first is alignment tools http://www.altium.com/documentation/15.1/display/ADES/PCB_Dlg-AlignComponentsDialog((Align+Objects+(PCB)+))_AD Note the object you select first is often what the other objects align for. Alternatively, I double click the object and modify its x or y directly. This is a little cumbersome but its very accurate. Knowing exact x and y coordinates helps keep everything inline.
