Starting in AutoCAD 2006, you can specify a highlight color and opacity to your selection areas as illustrated by the green area shown in the example below.
Below is a description of these options and how to change them.
If you want to go through the OPTIONS dialog, open it up and switch to the Selection tab. Click on the Visual Effect Settings button. Everything you need to control is there on the right half of this dialog, shown above.
Read more about Selection highlighting in AutoCAD
In AutoCAD, you can assign a non-continuous linetype to a 3D polyline, but it will not display or plot.
If you need 3D polylines, and you need a non-continuous linetype, for example to represent the flowline of a ditch - there are a couple of workarounds. Both assume that you have assigned the correct linetype to your 3D polylines.
Here is a quick guide on setting up a layout (or paper space) for plotting in AutoCAD 2000 and later. I used AutoCAD 2008 for these steps, and most of these steps should apply (except for the viewport locking) in all versions, 2000 and later. I know this looks like a lot of steps, but it's really easy. The best part is once you set up a layout, you never have to do it again. You can import this layout (or any other) into any other drawing.
Read more about Layout (paper space) tutorial: Part 1
This is one of the new commands in AutoCAD 2008 that is sort of overlooked, but can save you a lot of time. If you use xrefs, then how many times have you had a problem with the parent drawing crashing? You might try running AUDIT or RECOVER on the parent drawing and find there are no errors, but you continue to have problems with this drawing. Read more about RecoverAll