How many times have you seen lavender been neglegted and it gone long, woody and is lying on the ground. Well this is because it has not been pruned, and Lavender needs to be pruned hard, its from the meditteranian area originally, and there they got goats every where, which chomp down on the lavender keeping it in good short order.
Wording from RHS website: Left to their own devices, lavender can become woody and ungainly, so to keep plants compact and attractive, it’s best to trim them annually in late summer, just after flowering has finished. Remove any spent flower stalks and about 2.5cm (1in) of leaf growth. Foliage can be clipped over in spring if growth is untidy or frost damaged. Lavender does not break new growth easily from old stems so don't cut back into the woody stems.
As we do not live in a perfect world you will find yourself having to cut into woody stems to get the shape back, the way I do it is I would cut part of the lavender plant into the woody stems leaving most of the plant still maintaining this year new green growth, if the woody stems re-generate allow them sufficient time to establish new leaves and then you can reduce another small part of the plant. So if you have been gardening for a bit, then you will know there are two key things you need, firstley plan your pruning time to fit the plant and secondley, patience and a lot of it especially when trying to rejuvinate an old plant.