The first thing to consider is what you're wanting out of the process- creating art or doing design work where dimensionally accurate renderings are important. For me it's the latter.
I need to draw and sketch pretty much daily as part of the design process in my work (custom furniture)
Charles Freeborn Fine Furniture and Accessories – Handmade Fine Furniture and Accessories . For me it's more of a chore that needs to get done in order to communicate to the client or as part of my visualization process when I'm working out how to fabricate something.
Way back before I drew on the computer I took manual drafting classes for those basic shop drawing needs. I'm still a reasonably good draftsperson, although my lettering still blows - never was good at that. Once, when a client was having trouble visualizing in plan and elevation, I got a set of perspective charts - just came across them the other day... They were 2 & 3 point at various angles of "perspective". You use them as a background layer with translucent paper on top.
Then I began drawing with CAD - only 2d for many years as affordable 3-d wasn't around yet. When I went to furniture making school (Wendell Castle in Rochester) we had a drawing and design class. The textbook was "Rapid Viz". I still highly recommend that as a quick route to being able to do basic perspective layout and renderings. It's soft cover - really easy to get into and follow. Begins very basic and goes to very involved. I think it's essential to be able to quickly sketch in perspective for your own purposes and especially if you're in design meetings with clients.
Now-a-days I do my quick sketching by hand, then go to the Mac and work in Form•Z, which is a 3-d modeling program that can output 2-d views to scale and dimensioned. I can also take photo images and turn them into surface "textures" - which means I can put a piece of wood on my scanner, get an image and then apply that woodgrain to surfaces in my drawings.
As for the skill of drawing, it's like any other muscle memory. Takes a big chunk of time up front to get the skills, then constant practice (daily if possible) to keep your chops up.
-C