When cutting wood do you add the width of the blade after the line mark?
A circular saw isn't a super precise cutting tool so you'll want to keep that in mind.  Lining the notch on the shoe is not going to give you super accurate cuts.  Its fine for framing but may not be for other tasks.  

To me a cutting guide is the best way to improve your accuracy.  They are very cheap and easy to make, and they speed up your work quite a bit.  

Here's a link to one of many how-to's:  making a cutting guide



If you make your marks on the waste side of the measurement, you can quickly and easily line up the guide to the edge of the mark, and get a pretty darn close to perfect cut quick and easy.