Just reinforcing, its not about how good you are at artistically drawing. You don't need to know this (although being able to draw roughly straight lines will help), but its about knowing in your mind where to draw the lines.
What in particular is it you are having trouble wiht? Is it being able to construct orthographic views (front, side, top, etc) from a pictorial (where you can see more than one of the three principal faces from one view). Or is it going the other way, you can't visualise what the object looks like in 3D from an orthogonal drawing? Or is it smaller technical details you are having trouble with such as when you are drawing a section, you don't section webs and supporting members, or is it all the details of how to draw nuts and bolts.
From the sounds of things, you seem to be having trouble with all of these things.
The thing is you can get whole books on technical drawing, but it is only one part of the Engineering syllabus. However from experience (mainly past papers) there are only a couple of things that an Engineering student must know,
- how to draw and orthogonal drawing from a given pictorial and vice versa
- how to draw a sectional view, including the fact that you don't section webs, and different parts have the section lines going in different directions
- you need to know the different kinds of lines, i.e. the solid line ____ for most lines, the hidden line - - - - - - - for parts that are hidden from view, and the centre line --- - --- - --- for showing the centre of a circle
- you should also have a good idea of how to draw nuts and bolts
- you should be able to apply simple dimensions to your drawings, circles (R2 for radius 2 and \O where the slash goes through the O for diameters) and lengths are the most common
- you should know at least the 2 projections, orthogonal and isometric
What I would suggest is you try some past paper questions. I've put some samples below. If you have any more questions feel free to ask.
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Samples:
Try to look at these and try to understand them, and just get a feel of them. For the orthogonal ones (i.e. the ones with three views, from front, side, top, etc try to picture or even draw what it would look like in isometric. take a look at the isometric ones as well.)
orthogonal:
isometric (which is a type of pictorial):
shows 1st and 3rd angle orthogonal:
nuts and bolts:
sections:
dimensioning (don't worry about all the tiny details in this picture, but just get an idea of the key features):
Most of these were taken from here,
http://www.boredofstudies.org/wiki/index.php?title=Focus_Area:_Graphics_Industries
so I would advise you to skim through here and read some of the explanations. But remember that this link is focused towards a different course, but Engineering a lot of the things mentioned are relevant to engineering students (such as AS1100, use of CAD vs manual drafting).
oh, and if you want some past paper questions with drawings, just pick out some drawing questions from here
http://www.boredofstudies.org/view.php?course=33#33.4
