You don't want to get a book to tell you how to identify trees. Get a tree guide book like the ones recommended and it will describe the form of each tree.
Up front I can tell you the leaf form (colour, shape: compound or simple etc), leaf growth (deciduous? Do they grow opposite: Pairs like Acers; alternate: One on one side, then the next on the other, or whorled?) bud (form and growth pattern, ie clustered, sticky, round or pointed), twig (colour, is it hairy? Or shiny?) flower (is it wind pollinated like Alnus or insect pollinated like A hippocastanum?) and finally fruit (gymnosperm, angiosperm, fleshy, etc)
Get some trees you know you know. Get a sample each season so you can identify them the year round. Use the tree ident book to understand the terminology (pinnate, cordate, palmate, glaucous, glabrous etc) and label a tree that you know you can identify. When you can dissect and annotate trees you DO know, you can move onto those you don't. Seriously, books are the worst way of learning these things.
Authority: Forestry student first year who gets full marks on his tree ident tests. I know the Latin names of about 50 trees or more, and about 30 shrubs.