Here’s one that has been around for a long time, but I was just recently inspired to add it to my list of commonly used shortcut keys. In the Drafting Aids toolbar there are three buttons for drawing constraints (the three right icons in the second row of the image below). The first is a parallel constraint, the second is a perpendicular constraint, and the third is a special snap point constraint.
The inspiration for creating these shortcuts actually came from D’Genaro, who demonstrated using the special snap point constraint to quickly place an element at a designated midpoint. Normally I would just place it in one location, then move the element to the midpoint.
Using the special snap point constraints, you select the tool or element to be placed, select the special snap point constraint (or shortcut), then two click to draw the distance the element should be centered to. The element will automatically be placed to the center point (or other special snap point divisions) between the two click defined distance.
The parallel and perpendicular constraints can similarly be used to keep lines, polylines, beams and walls perpendicular to existing elements. Simply start drawing the element, click the constraints button or shortcut, then select the existing element you need to draw parallel or perpendicular to. You will then be limited to drawing the element to that axis. Use Shift+R to define a specific distance as usual.
If you are working on any basic modeling or drafting pull up the Drafting Aids toolbar and play around with these functions; after a short time getting used to them you will find a greatly increased efficiency at modeling & drafting. Set up some new shortcuts for these options. You may, like me, find that you use them very regularly now. My shortcuts for these are Com+1, Com+2 & Com+3 so that I can keep one hand on the mouse and still hit the shortcuts with just my left hand.