if you are sighting in free hand, its a big waste of time and money. you should definitely sight in with the sturdiest things available to you...a bench or sled...
shooting at a live target free hand isnt a good idea, but i have done it before successfully.
sticks, or a tree as mentioned, are a good way to go if ya dont have a table (if you will)
main thing, imo, is that when shooting, whether from a bench, sticks or free hand, is that you dont let anything touch the barrel of the "gun" as to not mess with the moa. if yer barrel is resting on sand bags at the range, it isnt gonna shoot the same when something IS NOT touching the barrel in the field.