My engine doesn't idle all that smooth and I need some help. ?

I have a 1999 ford f-150 4.2L v6 and it is in need of a lot of engine work I'm sure but never had a problem It has 120 thousand miles in it and no clue what kind of maintenance it's had just bought it last summer and the engine idles very ruff and I need help on how to fix it I'm very capable and not paying a mechanic to fix it if I can do so myself.