We all have had this issue, so you are not alone. Best tip is to take a spare sheet of paper or even newspaper and place it over your drawing even on blank parts of your paper to prevent any oils from your hand on getting on the paper. only leave the part of the paper you are working on uncovered. This helps create a clean surface for your works without smudging in the slightest.
A maul stick can also be used, often sold at fine art stores or made, it helps to put your hand down on and can be used for a verity of arts and often used in painting. I purchased a solid metal maul stick from amazon and absolutely love it for all my drawings and paintings when I am working on a easel or any upright position, if flat on a table, I will use the paper method. Hope this helps you with your work!