I've seen bite pressure questions pop up a lot lately, and I try to answer them as often as I can since I remember not too terribly long ago searching for those answers myself. So for any who have already heard my answer, hope I don't sound too much like a broken record. Lol!
People have a variety of different techniques that work for them. Personally, I've had the most success using the wobble technique. Basically, good beak pressure is rewarded with continued interaction and praise. (Remember that parrots, to varying extents, tend to be "beaky". They don't just use their beaks to bite. They also use them as grasping appendages, much like we do with our hands.)
But the instant that beak pressure becomes uncomfortable/borderline painful, you tell him"no" in a firm, yet calm, voice, and you give the arm he is standing on a wobble. (Only use this for bites and uncomfortable nips. Be careful not to punish beaking.) It is very important that you only give enough of a wobble to threaten your fid's balance, rather than to make him actually fall. Causing him to fall would likely damage the trust between you and set back his training.
Another thing to remember is that you have to keep your reaction subdued. Any kind of animated reaction won't necessarily be taken as a negative by your parrot. In some cases, your parrot might find your reaction rather amusing and attempt to elicit it from you again... leading to MORE biting rather than less. "Look at what I can make my human do! Ha!"
Even done right, this technique isn't an overnight fix. But done with consistency and patience, your bird will eventually come to associate harder bite pressure with an undesirable loss of balance. Hence, a negative thing. And the word "no" will come to mean something negative for him as well. In time, the wobble would no longer be necessary. Just saying no will suffice.
And just to cover the gamut, if he does manage to latch onto you pretty hard, I'm not one of those who advocates completely ignoring what's happening and taking the pain. (Ouch!) Keep your reaction subdued, yes, but don't let him just gnaw away. First, push INTO the bite. Counter-intuitive, I know, but pulling away will often result in worse damage. Then, using the thumb and index finger of your free hand, grasp the beak on either side of the tip and firmly (but GENTLY) leverage the beak away in a slightly twisting motion. No wrenching. Consistent pressure only so you don't hurt him.
And lastly, as for your fid's newly discovered tongue and his desire to use it extensively... sorry, can't help you there. You just have to live with the fact that your bird's a little fresh
