Select should hide your UI, then it's L1+start to screenshot. I'd also recommend setting your movement type to Legacy, because it's the superior and correct option, and also enabling your extra crossbars.
The way it works normally, you have either LT or RT. Expanded Crossbars allows you to open up two additional bars by holding LT and then pressing RT and vice versa. It gives you a wealth of buttons to play with, and if you play an active class with a lot of demand while moving, it opens up twice as many "face button" commands. Running with your left thumb and then needing to hit the d-pad to activate a skill causes you to stop running! No more, thanks to Expanded Crossbars.
/commercial
The way it works normally, you have either LT or RT. Expanded Crossbars allows you to open up two additional bars by holding LT and then pressing RT and vice versa. It gives you a wealth of buttons to play with, and if you play an active class with a lot of demand while moving, it opens up twice as many "face button" commands. Running with your left thumb and then needing to hit the d-pad to activate a skill causes you to stop running! No more, thanks to Expanded Crossbars.
/commercial