Q:

Looking for a 'quick-and-dirty' resource for proof techniques

I have limited time to spend on the resource (3-6 hours) and never done any proofs and I need to be able to apply deductive, inductive and other proof techniques to some relatively easy propositions (basic number theory, trees etc.).
Please recommend a resource (website, or short book) that will meet these objectives.

A:

The following books will be of use for you:

How to solve it, as David Wallace mentioned.
(geared towards contestual math) The Art and Craft of Problem Solving
How to Prove It (this could be used by anyone in highschool or a bit before)

For basic number theory stuff you have several options depending upon your background:
If you don't have any abstract algebra, then I would reccomend Elementry Number theory by Strayer. It does use some algebra, but very little. There is also the Rosen book, which is widely used. Rosen is supposed to be simple and straight forward. 
For graph theory stuff, any introductory discrete math book would be fine, enless you want to learn a lot about the subject. In the case that you do want to learn a fair amount about it, then I would reccomend Graphs and Digraphs by Chartrand, Lesinak, and Zhang. The 2nd option is much more involved. You can also find plenty of free introductory number theory books online, by googling "free number theory." Apperently, number theory is stuck in jail.

