Mieszko Grzeszczuk
Mieszko Grzeszczuk voted up JNicka Nicka's answer

I always followed Happy's advice.

And as I introduce myself.  First and last name. If its ok people call me _______. Thank you.

Mieszko Grzeszczuk
Mieszko Grzeszczuk voted up HappyTwo BeHereTwo's answer

Good for you! I always wrote my legal name on the forms.

First Name:  HappyTwo  Last Name:  BeHereTwo

If a place for your preferred name isn't provided, you can write it parenthetically.

First Name:  HappyTwo (Happy)  Last Name:  BeHereTwo

or just verbally introduce yourself that way. 

Good luck!!!