Re: accurate straight lines
I assume you are talking about print output.
The more detail you use in your work onscreen is also reflected in print. Vector drawing takes practice, you often have to go back and refine parts you have drawn with added nodes or changing the node types.
Drawing is in itself the best teacher and doing tutorials. Click 'n Learn offers some great free and paid for tutorials, also Unleash.com.
You also learn how the DRAW engine "thinks". More logical than Adobe.
Re: accurate straight lines
Hope I can help :)
Please make sure these following condition.
a. never make you line in hairline thickness, make it thicker. say at least 0.3 mm
b. use the guideline to make your straight line
Good luck