It is all to easy to have little particles of spit hit the paper!
Brush your paper clean.
The best way is to use a soft bristle brush.
Any soft bristle brush will do.
I use a draftsman dusting brush which can be found in all good art stores. (I like the size it covers a wide stretch of my drawing in one swoop!)
Never blow on your work to remove eraser debris or dust but use a fine bristle brush.
In case you've mist the first few SDTs, here's where you can discover more:
Short Drawing Tip #1: Paper Choice
Short Drawing Tip #2: Warm-Up
Short Drawing Tip #3: Protect your Paper