Where to place theta when resolving forces into components

[AirForceOne]

Hi,

When drawing the FBD (ex. block on incline), and when you split a force into x and y components, where do you put theta when giving the angle of let's say, the incline? Is there a trick to this? I generally know where to put it (basic trig), but for some reason I can't use trig for some other forces.

 

[Mark44]

Theta (or whatever you're calling the angle) would most likely be the angle the incline makes with the horizontal.