1. I'll keep my fingers crossed for you.
[Do we have to use the fingers of both hands? Or do we use the right fingers alone? Do we have to show the back of the hand or the palm of the hand in this case?]
2. I'll cross my fingers for you.
[Is this one the same as #1? Do you use this expression frequently?]
1. I'll keep my fingers crossed for you.
[Do we have to use the fingers of both hands? No, only one hand. Right or left, it doesn't matter. Or do we use the right fingers alone? Do we have to show the back of the hand or the palm of the hand in this case?] Usually this is just a saying, meaning, "I wish you good luck." But if you actually show someone your crossed fingers, you'd probably hold your hand up with the palm facing your friend.
2. I'll cross my fingers for you.
[Is this one the same as #1? Do you use this expression frequently?]
Yes, this is the same as #1. You could use either expression. And if someone REALLY wants to show emphasis, s/he might say, "I'm crossing my fingers and toes for you!" (Of course the latter is impossible, but if anyone says something like that, s/he simply is emphasizing the idea of wishing someone good luck.
1. When saying "I'll keep my fingers crossed for you," the most common practice is to use the fingers of both hands. However, it is not necessary to show the back of the hand or the palm of the hand while saying this expression. Simply intertwining or crossing the fingers of both hands will suffice. It's more of a symbolic gesture expressing hope or wishing good luck.
2. Yes, "I'll cross my fingers for you" is essentially the same as the first expression. Both expressions convey the idea of hoping for a positive outcome or wishing good luck to someone. The second expression is also commonly used, often interchangeably with "I'll keep my fingers crossed for you." People use these expressions to show support and convey their optimism towards a particular situation or outcome.