According to that wikipedia article, serum is 60-80 ug/ul in total protein (mainly albumin and immunoglobulins). If you want 20 ug in 10 ul, the protein concentration is 2 ug/ul, a dilution of 30-40-fold, as Artur Burzynski said. Most of that protein will be in a single band of albumin and about 66 kDa, which will probably cause some distortion in the gel. There are resins available that will reduce the albumin content of serum, allowing more of other proteins to be loaded onto the gel. Here is an example:
Your loading buffer should have glycerol and beta-Mercaptoethanol. Glycerol reduces the clotting and b-Mercaptoethanol targets disulphide bonds to reduce tangles.