The "push/pull" set up for the triangle choke is one of the easiest ways to start working on triangles. Here's a quick lesson on how to set this one up, along with some finishing details.
Start with your partner in your closed guard. Control both wrists with your hands, with your thumbs facing down. Push your partner's wrist into their belly button, while simultaneously pulling with your left arm, aiming somewhere around your head. As soon as your partner's wrist is pinned to their stomach, keep this pressure on while you open your guard, lift your hips up over their (now trapped) arm, and then cross your ankles once again. From here, you just need to make a few adjustments in order to finish the choke. First, drag your partner's arm across your body (keep in mind that their own shoulder will choke them on one side of their neck), and then "bite down" with your right leg around your partner's neck. The idea here is to be able to grab your own shin, preserving this right angle bend in your right leg while controlling their posture. Once you have your shin, you can step on your partner's hip in order to angle your body out as close to perpendicular as you can get. Be sure you have a tight figure-four leg position, and squeeze your knees together for the finish.
For a more detailed look at the submission itself, see How to Finish a Triangle Choke.