Ruby main here, 200+ games with her.

The three lifesteal items mentioned above are key. Ruby does less damage than other tanks but has good sustain and amazing CC. She has good survivability when alone and great contribution to team fights.

General tips:

-poke with S1 -be sure to use her movement abilities after using her skills -I always use flicker as my spell -try to take advantage of solo fights and team fights that have minions around them. Use S1 and S2 on as many enemies/minions at a time to get that sweet sweet lifesteal -when facing multiple enemy heroes by yourself, sometimes (but not all the time) it is actually more advantageous to S1, dive into the enemies, then S2 to refill your health before retreating/waiting for teammates -most people initiate with her ult, but sometimes it’s good to save it. If your tank or whoever already initiated the team fight, go in with S1, dash forward, then use your S2 to CC. Usually your teammates will drop all their CC at once, and sometimes the enemies can still get away after the initial stun. This is when I use my ult - when they are lower on health and have decided to start retreating. Pull them back to your team and let your team finish them off. -practice the flicker hook in vs AI mode

Good luck!