I like 'The Inner Game of Tennis'
not technique stuff at all, but useful.
I taught myself to play with 'Lawn Tennis the Australian Way' as a child, but I don't think it is relevant anymore.
5.0 all courter. 2 x Dunlop Bio 400T with cyclone @ 50, 1 x Dunlop Bio F400T gut @ 55
"Tennis isn't easy" - Corners