Here is some of the tip I figured out when playing CC:
1) Stick to the crystal: your not a DPS and that is a fact, yes you can do some decent damage but stick to the crystal since you have more HP than any other job in CC and can take the hits.
2) You dive in first: when you are retaking the crystal or makeing first contact you want the other team to focus on you first while the rest of your team can do damage and do as much damage as you can. yeah, you might KO, but it will put them on notice and force them to adjust fast!
3) Positioning is important Position where if you're contesting the crystal or defending it you want to be in a position where if you can LB and get the most targets and also keeps others from sneaking up on you. Usually, stick close to a wall, if the crystal is at an intersection stick to a corner, positioning is important. Keeping you back to a wall or corner so you can keep an on on things while staying inside the crystal's ring is important.
4) Use your healing pot where there is a lull in fighting You won't have many opportunities to get healing pots on the field so when you have the chance sneak away if you can pop your healing pot and go back into it. make sure you are not seen or around other teammates as well as the other team might come that way. Also, make sure someone on your team is on the crystal when you pop your pot so the crystal keeps moving forward or is being contested.

*Side note for WARs: If you played Overwatch play it like your Reinhart. Yeah sounds weird but It works when a WAR diving in with a Primal rend and stunning a load of folks at one! you will force them to use there anti CC skills right away, then follow up with Orogeny then blood whetting/steel cyclone combo you will get most of your HP back for the HP you lose in the process but spam your CC skill and heals as your going to need it.

These are just some of my observations for playing tank on CC, is by no means a must to do, just something I picked up playing CC.