Not so much the doing of the spacework. Mostly that's pretty good, as long as you remember that your index finger is not technically a gun.
Where it tends to fall apart is in the remembering of where objects are located. I have seen people walk right through horses, desks, dead gangsters, you name it. I've seen people type letters on their barbecues and put milk away in the broom closet. Once you've created something in the space, remember that it's there!
It'd also be awesome if you could remember the objects that are in your own hands. If you're holding a baby, remember to put it down before you fling both of your arms up in the air in frustration! Otherwise, the entire audience will gasp and wonder where the baby landed. If they're worried about the baby, they aren't listening to your amazing information. Don't sip your coffee, then use both hands to strangle your coworker, then go back to sipping that same coffee, unless you thoughtfully set the mug down on the desk before commencing the strangling. If you or your partner inadvertently drop a spacework object, call it out! "Dammit, Marco, it's bad enough you're strangling me, but you broke a mug and spilled coffee all over the carpet, too!" The audience will have noticed, so when you acknowledge the error they will feel vindicated and reward you with laughter.
You can get away with pretty much anything in improv, of course, as long as you justify it. So when the spacework errors occur, just justify them and move on. Unless you've walked through a horse. There is pretty much no justifying walking through an entire horse, people.
By Sonnjea Blackwell