I love step by step instructions with a picture ( Photo or drawn) of each unit and the size it should be before finishing.
Lots of patterns have finished sizes for units and blocks which makes no sense to me because you have to have the unit sizes right first.
Some patterns are made in a certain style to look hand done and homey but sometimes they can be very confusing and hard to follow. I do like this style, like it is grandmas own handwritten copy of a pattern, but they should be well thought out.
A chart for fabric amounts
A chart for cutting
I also like patterns that tell a story or have insights and jokes. I am not into serious perfection.
Hints on making or giving your pattern a personal touch. This gets people thinking and being creative with just a little information to get them started.
I do hope you give pattern writing a try and I would certainly volunteer to try it out!
peace