How can I improve my skills in engineering drawings?

first thing is which type of engineering drawings u r referring to ? if you are an Architect first u must know how to read the drawing what architect is trying to deliver and also a simple person or layman can read the drawing easily (non technical drawing) and practice makes the man perfect

No matter what field of engineering you are when making drawing presentation, assume yourself to be the user of the drawing or the one who will execute through this you can check by self if it is executable or not.
Also drawing is a form of communication try to present it simple and complete so that the user willl easily understand your message.
Read also other references available in the net.

1st you have to spacify which sector in engineering you are talking about as every part has it's own programs and also has it's own methods in manual drawings.