maybe keeping there arms crossed or covering their body. Usually if you are being open, you're hands are open- if that makes sense.
Also a dead give away is obviously if they blush.
depends if theyre a seasoned lier or not and who you are to them. if you're not important and the lie isn't you can spot it a mile off...if they care about you they will try and be more convincing and you might want to believe them too. that whole negotiator 'look to the left is a lie....' it takes a long time to be able to detect small changes. also if someone believes their own lie their reactions will be that of telling the truth...it's very hard unless you can lie well yourself to see if someone's telling a porky..
One way is to follow the person constantly, use mind scanners to find out what they're thinking and ritually subject them to torture and beatings. if you don't find out if they're lying that way, you'll never be able to tell.
if they look up it means they are searching in their brain for somethign to say.. or something. and also if they cant look you in the eye, thats normal. think about it, when you have conversations with people about something totally normal, you dont look them directly in the eye do you? keep a LOT of eye contact shows they are aware of lying and want to cover it up by maintaining eye contact with you.