Is the system in Equilibrium or is there an acceleration?
The key to solving motion problems is to draw an accurate Freebody Diagram containing all the information given.
Is the system in Equilibrium?
If not, then the Sums of the Forces will be equal mass x acceleration.
Is there Friction to consider?
Sums of Forces
A fundamental interaction is a mechanism by which particles interact with each other, and which cannot be explained by another more fundamental interaction. Every observed physical phenomenon, from galaxies colliding with each other to quarks jiggling around inside a proton, can thus be explained by these interactions. Because of their fundamental importance, understanding of these interactions has occupied the attention of physicists for over half a century and continues to do so.---WIKIPEDIA
The Problem to the right
is an Animated Problem
Here is the actual pdf
