Basically, don't pick an MOS that starts with 11, 13, 18, 19, 27, 36, 42, 56, or 92. These are all either combat MOSs or essentially desk jobs.
Other than that, career fields that begin with 12 (engineers), 14 (air defense), 15 (aviation), 31 (law enforcement), some 68 series (medical), 88 (transportation), 89 (ammo and explosives, 91/94 (maintenance) are usually pretty hand-on, non-desk type jobs.
What I will warn you of however is that all soldiers are soldiers first. I was deployed with a guy who was a 42A (human resources assistant) who was also the M240B gunner on the commander's truck. You can try to pick a job that will keep you away from combat or desk work, but you don't get that lucky with assignments. I know of infantrymen who get stuck in the mailroom for years at a time and similiarly "desk-type" or "leaf-eater" types that have been put in line units where they deploy and see combat quite often.