I personally wouldn't recommend Inkscape for technical drawings. It's much of an hassle to get everything just right.
Inkscape is more vector drawing oriented.
What I would suggest is Google SketchUp. It's quite easy to use and suits better for stuff that requires drawing accuracy.
Also combining both of them might be a good idea. The objects that require precision do in SketchUp and later combine them in Inkscape with additional artwork (eg. hands, text).
- SVG plugin for SketchUp, is a nice tutorial how to combine Inkscape and SketchUp
Very good book Inkscape: Guide to a Vector Drawing Program (there's the free web version and the book - I highly recommend the book, it really is worth the money). It explains quite nicely Inkscape from beginning to end with nice examples.
Must read chapters for technical illustrations in there are: layering, sub-layering, connectors, tracing bitmaps and isometric projection.
Learn how to do diagrams. Basically you should know how to use clones properly.
How I usually do those kinds of illustrations is:
- Draw (with a pencil) a basic outline what I'm going to do.
- Then import that into Inkscape and draw all objects with really simple shapes.
- I don't draw one thing twice nor do I duplicate it. I clone it - it has a nice feature that when I change the original all the clones change.
- Usually I keep the originals off the page and use only clones on the page. (of course if there's more than one object of that type).
- Then do the generic outline with all the things
- Finally add the text to separate layer.
Also it's quite useful to have "library" of objects in a .svg you often use.