House Decorating Guide: How to Move and Drag Items to Customize your Skyrim Home
Why the Hell Does the Cursor Always Grab the Item in the Middle?!
This is probably the biggest hit the move / drag feature has taken to its versatility - in past games, you could pick up an item at the point which your cursor was targeting, allowing greater freedom of movement when placing the item. Unfortunately in Skyrim, targeting an item with the move / drag feature will almost always force it to be grabbed roughly in the center, which severely limits your ability to place it the way you want to. To compound this problem, many of the game's items are 'weighted' counter-intuitively, or at least inconveniently - some pots and bowls will always want to turn face-down, for instance, which is generally not how you would want to place them. And God help you if you want to have a few sprigs of lavender standing upright in a basket.
It's just something we have to deal with, unfortunately - get into the habit of using walls and corners built into the cell to change the position / direction of the item you're holding, rather than just shaking it around until it gets in the right position. If walls / corners aren't handy in relation to where you want to place an item, you can try stacking other, larger items near the spot and using those to reposition the item.
If you have the item in place, say on a desk or shelf, but want to fine-tune its positioning, do not try to grab it with the move / drag again, as it will usually be yanked towards you, which will disrupt the placement and possibly knock over any items next to it. Instead, drop another item, pick the new item up with the move / drag, and use it to fine-tune the position of the first item. Rings are very reliable items to use for fine-tuning placement, as they are small, symmetrical, and most importantly, aren't usually affected by the problem of other items causing said rings to fall out of your grasp...which leads me to my next tip...
Why the Hell do I Keep Dropping These Items When I'm Trying to Place Them?
This isn't a new problem (Fallout 3 and New Vegas both had it), but it does seem worse in Skyrim - occasionally when you're trying to position an item, it will drop out of your grasp when it comes in contact with another placed item. The extra insult is that if it stays touching the item that caused it to fall out of your grasp, it will often prevent the move-drag feature from picking it up, and you'll either have to move it away by holding another item, or pick it up into your inventory, re-drop it, and leave the cell to use it again.
If this happens, use the aforementioned ring or similar item to 'push' the stuck item away from the items touching it - as long as the stuck item is clear of the other items, you should be able to move / drag it again. Or if that's not an option, you'll just have to take it back into your inventory, re-drop it, and decorate with it when you re-enter the cell.
This problem is usually confined to certain types of items, fortunately. Flowers (lavender, tundra cotton, etc) are the biggest offenders, followed by candlesticks and goblets; other items are capable of this, but these are the ones that give me the most trouble. If you're able, try to place these items first before placing other items in around them. Obviously this won't work with flowers, as you'll generally want to place them in a bowl or pot - just make sure you have them positioned just how you want them before dropping them in, and don't get too nitpicky with their placement, otherwise you'll pull your hair out over something that already has strong potential for being very frustrating.
And since we're on the subject, note that - ironically - flower baskets have no negative space and can't have items placed inside them, but regular baskets - including the ones shaped like flower baskets - can.
Simple questions deserve long-winded answers that no one will bother to read.