Most spots/blobs are uneven development and/or drying. A good pre-wash will help the development issue, and a good pre-dry squeegee can help reduce water spots. I find 35mm is especially problematic when drying. When I started doing colour processing, in which a pre-wash is a necessary step, I really started to notice the difference it can make.

Careful how you handle the film when loading it onto reels, and what it comes in contact with in the process, so as to reduce finger prints/dust. However, I find dust on the scanner is generally a bigger problem than on the film itself.

I agitate for the first 30, then once a minute. If you're not using a stock developer solution, make sure the working solution is mixed well or else the concentrate may be mostly sitting at the bottom of your graduated cylinder when you start to pour.