In order of importance:
1. Title name!
Contrary to popular belief, people DO judge books from their covers. People like to see either 1 of 2 types of guide names. There is the mathematical elitist one that usually looks like "AP Stacking Teemo w/ DMG Chart" and there is the themed creative one that usually looks like "Brewing Insanity - A Guide to Singed". These titles will often catch more eyes then simply "very good ashe guide"
2. Layout and Neatness
People tend to understand things more and be able to actually read text easier if everything is ORGANIZED. I think I speak for everyone when I say that looking at a block of white text almost immediately makes me want to stray from reading the guide at all. Things you should do to make a guide look more neat? Use lists, points, small tips, and use quote boxes.
You know it was coming, content is essentially what people came to your guide for. A lot of guides I see have the basics, comments on skills, skill build, recommended items. However going above and beyond the norm is what makes a guide stand out. Synergy with specific heroes, How to utilize specifically one skill to it's maximum potential, and explanations on the numbers behind a skill can be godsend to the reader.
Although I like to read the occasional 'Massive Super In-Depth Guide with 10 Line Graphs', most of the time I don't. There are two guide sizes that I love. There is the 'Average Joe's Basic Needs' which is not too long but not too short, giving the details that you need and there is the 'Quick Stop 'n' look' which is essentially a skill build, item build, and very small commentary on skills, which explains a SPECIFIC build for a champion. The latter usually ignores what I previously have said on content but sometimes short and simple, when executed well, works wonders.
5. Edit, use it.
Simply put, if someone gives you advice or if you think something needs sprucing up, just use the edit button. It's there for a reason and it's not like once you post a guide, it's final.
Thanks for reading, I kind of just got bored