You could try drawing it at 1:1.
I do all of my drawings at 1:1 in MSPaint. If they come out too fat(Like my first ESB), I then resize the width in Photoshop, and then try to clean up anything it made look less detailed.
I used to add clouds/sun-glare in MSPaint(The last drawings I did entirely in MSPaint was The Chrysler Building and Woolworth), but it just got too time consuming...so I do that in Photoshop now.
You don't need a fancy program to make a nice drawing though. The last diagram I did completely in MSPaint was this: