Metals are contained on the left side and center of the periodic table. The first two groups are metals. The next ten groups are called the transition metals. Finally, some of the elements to the immediate right of the transition metals are also considered as other metals. Generally speaking, reactivity among metals increases moving down and to the left on the periodic table. Reactivity increases when moving down due to the fact that the atomic radii increase and the valence electrons get further from the nucleus and are therefore easier to remove and react. Reactivity increases to the left since there are fewer electrons in the valence shell and that makes it easier to remove one of them. So the net effect is that the metals to the upper right of the periodic table are the least reactive while the ones on the lower left are the most reactive.
Just keep in mind as you go left to right on the periodic table the reactivity decreases (because of the increase of electrons on the outer level).
And that as you go down a column on the periodic table the reactivity increases due to the fact that the atomic radii is increasing, and the electrons are moving further away from the nucleus.