Take it SLOW.... that just can't be stressed enough.
Taper dosage by no more than 20% at a time and step down every 4-6 weeks. There are loads of posts within this board about tapering methods. (counting beads if capsules, cutting pills)
Will it take a while (12 months or more?) YES! Will it be worth it? YES!
Withdrawal from Venlafaxine is debilitating for some.
Best wishes!