how do you approach someone you're crushing on?

[Lyssa]

em... ok so here is the thing ,,, I have been having some feelings for this girl, but the problem is, well she is my professor, actually was , but I'm still in college , we had some good times together like talked outside class and so on even discussed a lot of issues that she found of interest, so like I'm not sure how to ask her out given her position and the age difference (20 years aprox) , which don't bother me but I know it might get a bit sensitive, like I don't know. I have her phone number,email and we follow each other on twitter. I'm just a bit scared I guess,,, any suggestions? thanks!