Go into battle , then act like you are wounded and are retreating for medkits. Retreat jumping backwards or running backwards, but not too fast, because the soldier is slower than spies. Stay away from experienced players, and go for lone newbies. Veterans generally recognize spies more, especially spies disguised as snipers. Instead, on large maps, follow lone enemy players or newbies.
Newbies are easier to convince.
9.If you are diguised as the enemy, never start jumping in front of a foe as if you are dodging them as an enemy. Veterans notice this. I also notice it. When an enemy touches your dispenser, you'll get a warning. Hit the key you bound and blow the dispenser.