If he isnt the rebbe of your chasidic sect. You say sholom aleichem, plain, thats it. Then you should introduce yourself. If you want, you can add your mothers name too. If you give him a kvitel, ten just state your name and surname and where you are from. Give him a while to read, then he will raise his face. At that point you can address any inquiries or requests. This is general protocol.