Don't muck it up

muck 

n.

1. A moist sticky mixture, especially of mud and filth.

2. Moist farmyard dung; manure.

3. Dark fertile soil containing decaying vegetable matter.

4. Something filthy or disgusting.

5. Earth, rocks, or clay excavated in mining.

tr.v. mucked, muck·ing, mucks

1. To fertilize with manure or compost.

2. To make dirty with or as if with muck.

3. To remove muck or dirt from (a mine, for example).

Phrasal Verbs:

muck about Chiefly British

To spend time idly; putter.

muck up Informal

To bungle, damage, or ruin.

http://www.thefreedictionary.com/muck