Titan is one of those fights where healer threat is usually an issue. If you are doing FC runs or set up groups (non pugs) tell your healers to use medica I over Medica II until the last phase or absolutely needed. Medica II pulls more threat then you as a tank can build in more then 20 seconds in a single cast. So if it's being spammed you will not hold threat without using provoke. That isn't your fault, completely the fault of the healer that should know better.
Edit - Didn't see naaros' post above but same thing applies.
Other then that, pop fight or flight before pull as you always should and spam your combo. When he jumps hit em with shield lob before he gets to you. Should never have any issues with threat
On long fights it's better to establish your threat then pop Bulwark and spam Shield Swipe rather then Flash. Yes you use TP still but you gain more then you use. Use this 2-3 times through long fights and you never have a TP issue. Flash spam generally is a waste since just about all DPS will gain more threat then your flash's and riot blade combo's to gain that mp back.
Hell I'd rather throw out our gimped cure's then spam flash. At least there's some type of benefit from cure.