Resistance Band Tricep Pulldown: If you have a structured anchor point you can use that but you can also use a door! Open a door halfway and put resistance on top with equal length coming down. Grab on to a piece of band before the handle and pull down until arms are straight. You can stick one leg in front of you or keep them parallel. I personally have one leg forward to give me more of a base and to allow my arms to go down further. (You can also use this same technique on a cable machine if you have access to it.
Single Arm Tricep Resistance Band Pulldown: This exercise is great for isolating the tricep. Like the previous exercise you will use a door or another anchor point. Put a resistance band over the top of a door and close the door. Then pull the resistance band through until only the handle is on the other side. Pick up the resistance band and walk forward until you feel tension in the band use your opposite hand as a stabilizer and pull the band until arm is straightened.