Many people tend to have troubles keeping up WOTB on lower MPs (which are the best for farming XP and usually also for legendaries unless your DPS is super high). An easy solution is to switch to a higher MP, but then the runs become ineffective and inefficient due to the lower killspeed.
How to keep up WOTB in MP0 and 1 (for low budget builds):
1) Gear specifically for IAS and Critchance, try to get ~40k DPS (MP0) or ~70k DPS (MP1) unbuffed and IAS/Crit on as many slots as you can get
2) Don't kill every single trash mob. Focus on large groups of mobs
3) Use Bash Instigation in combination with Sprint Tornadoes and Whirlwind Spam for additional Fury gain.
4) Make use of objectives when there are no mobs around, quickly bash them. Use Warcry to bridge periods without enough mobs.
5) Permanently SPEND your fury! This means spamming battle rage and also sprint tornadoes, even when they are still up.
6) Don't waste time picking up all Rares - only pick up legendaries, rings, amulets, shoulders, gloves, bracers and certain weapons.
7) Use Boon of Bul-Kathos, if you still lose WOTB sometimes, use Animosity if you can have it up for an entire run.