How to Stay Afloat

Hi guys, recently I bought an O'Neill Gooru comp vest, it fits me well but I haven't tried it on water yet. I ride both on salt water and fresh water. I used to wear a thick comp vest though the JetPilot A-10, it worked very well. Once I've tried a comp vest before which I don't remember what brand and the water came up to my lips. Do you guys know how to stay afloat well wearing a comp vest?

Thanks a lot for the help before.

Cheers!