A: Your handwriting is beautiful. It's really unique!
B: You must be pulling my legs.
A: Really. You have improved a lot on your handwriting.
B: I know, I know. I'm keeping on practice, actually.
pull one’s leg
exp. To tease or joke with someone. （笑话某人，取笑某人）
e.g. Quit pulling my leg, I know there isn't a Hollywood director calling me right now.
e.g. I love pulling my sister's leg—it's almost too easy to annoy her.
e.g. Michael and Derek are good friends but they like to pull each other's leg sometimes.
keep on something：坚持做某事
e.g. How am I to work if you keep on chattering?
e.g. You'll soon go to pieces if you keep on working like that.
e.g. There would be vermin in many New York buildings if the landlords didn't keep on the lookout for them.