You can move items around on your farm by holding on to them until the up arrow fills.  Then you can move the building around and you will have options to cancel, bulldoze, rotate, box (only for decorations) and confirm.  Some buildings can not be bulldozed.  Your third best friend is the storage box for decorations.  You can store all your decorations, arrange your farm and then place all your decorations back down (5th tab in the build menu.)  Grouping things together helps your farm to run better.  On average, I can find 60-100 happiness just be rearranging a farm.  I find expansions in 2x2 blocks are easier to organize than odd numbers.