Well, it's not mandatory to consider other guides on this website. If you really want to create a guide and if you've got a certain amount of knowledge and experience you can create a guide based on what you know about a champion. Certainly, there will be things being mentioned in other guides as well but the overall amount of guides (the decent ones) create a collection of guides. There are often aspects/ details in guides not being covered by other guides. The decent guides will likely receive more views and feedback but you are not mistaken when simply publishing your own guide even when it's nothing completely new.

Not too awful for a first try.

You might consider adding more info to your "cheat sheet", there are tabs you can use to have more item sets.

As the person above said, this would greatly benefit from some coding. It's a little confusing to deal with, but if you make use of the BBC code guide above and just keep trying stuff out, you should be able to figure it out.

Also, you might want to take a look at some of the top Ahri guides out there. Figure out what's different between how YOU play Ahri and how they do, and tell us about it. If there's nothing different, you might want to reconsider making a new guide and instead just give feedback on other guides.

Looks good so far but like you already said you don't seem to have any clue about coding.

You only need to put [[ ]] those around the word. Then you have something like this Ahri.
I would recommend to use this code in your ability section so people can look up cooldowns or mana costs.

Example: =Passive - Essence Theft

Colorful headlines are also nice

Example: =CDR glyps

Look at spelling and after the period leave a blank. Or else it looks messy.

I think mastering Ahri is also about using spells at the right time to e.g. catch off people by surprise and also using auto attacks between spells to harass.

Something like how to come back from a losing lane or to know when you're the strongest is also necessary to take advantage of the enemy. Just some ideas.

http://www.mobafire.com/league-of-legends/wiki/mobafire/bbcode-guide

Thank you! this guide really useful. Great job for your first guide. Can you add some more about major matchup in midlane against ahri?