There are MANY ways to force a card which can be found on DVDs as well as books.
A very easy beginner force for newbie is simply the cross cut force, which done correctly with a moment or two of byplay and patter flies right by people.
Another beginner force you could look into is the Hindu Shuffle Force which can be done very easily and looks fair to layman.
A Slip Cut force is also useful but looks horrible if not executed correctly.
The Classic Force is a thing of beauty and will take you a VERY long time to perform it flawlessly. There are so many things that take place during a good classic force. One of the best I have seen is Anthony Gerard.
Another consideration...can you see the forced card? It does make a difference.
The riffle force is a good all-around force, as is the classic (if you get it down properly).
Basic forces (as Rick Everhart pointed out) are very deceptive if your effect/routine are structured properly.
for 1-5 people I would use a force where the spectator can touch the cards (Cross cut, classic...) but larger than that the riffle is good because you can pick someone who isn't right next to you to help and just tell them to 'say stop whenever..'
There is always forcing decks as well...but that'll depend on your effect (makes your ACR look like REAL magic!!!)