OP:
I honestly find lying incredibly difficult. I will agree with what IB said about 95% truth though... makes it especially hard to sift, and most people won't bother. You want the minimum change for the maximum effect, to minimise risk.
As for being a 'fast thinker'... perhaps, but only in situations where I'm not stressed, and finding the need to cover the truth does not fit the bill. I don't particularly like being persecuted either, but I've discovered it's easier with my conscience and just generally if I learn to accept all possible consequences rather than trying to run from them by obscuring the facts.
I don't have an unexpressive face either, such that even when telling the truth I often feel my face 'giving me away' (giving away what, what?!) - the Suicide Bomber Complex. Every time I go through security at an airport I'm convinced they'll find the bomb in my bag, the gun in my pants, the knives in my boots. I walk through the scanner - did they catch me flinch? Don't look, don't look! Breathe normally! Same thing when I'm, for whatever reason, accused of stealing or lying. I think it's perhaps a result of being too indulgent of possibilities - maybe I forgot I snuck her wallet, maybe the last bomb blast wiped my memory. Are you glaring at me with suspicion as I hurriedly search my memory? Fuck yo- careful with that belligerence! For god's sake don't shout JIHAD!
It's not really a viable option for me. (I should add that I'm a pretty experienced flyer; nothing's changed.)
Which isn't to say I've never lied - of course I have, and I do often try to fine-tune my own stories or others (more out of a freakish need to test defences), but they're on very rare occasions where I consider the information private - usually belonging to somebody else whose confidence I cannot break (and in situations where revealing I'm in their confidence compromises them) - or unimportant. I never lie in "important" situations. This includes anything where rights and safety is at stake. I don't cheat, steal or betray trust in other forms unless the information is useful and important only to me, breaks prior commitment but is generally harmless, or endangers another person needlessly.
I do say untrue things to gauge reactions sometimes though, but this is always followed up with acknowledgement unless I'm unable to (eg if the conversation changes). Generally it's just incredibly inane/ridiculous stuff meant as a joke, it's just that people don't get it/aren't listening/ignore it, so correction isn't really necessary.
Also, sometimes I can't tell if I'm lying or not. The harder I try, the more confused I am. This only really happens in areas relating to my mind/emotions though, not objective statements unrelated to myself. I've simply accepted it.
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A lot of people here (we've had a few lying threads I think) seem to consider themselves good liars. How are we gauging our success? Maybe other people see through it but can't be bothered to call you on your bullshit?