A job description is not a job ad. I cannot stress this enough. There is nothing more tiresome than to see an ad like this:

Requirements:

At least 5 years experience 
Ability to make swift decisions, work through stressful situations and solve problems quickly 
Deep knowledge of your area 
Creativity 
Ambition 
etc.

Does this make you want to jump up, tell your boss you're leaving and go work for this company instead? I don't think so. This hardly evokes an emotion, much less the feeling of wanting to uproot so much of your being and quit your job.

You have to remember that in the end of the day, that's what you want people to do. The people you want to apply are probably being treated really well at their current job so that they won't quit. So, you have to work extra hard to attract them!

Ask questions instead of demanding

Nobody wants to read a list of your demands. If you get a lot of unqualified candidates applying, make sure you use questions to filter them! For example, by asking how many years of experience they have, you will be able to filter the applications, and thus save yourself from reading a lot of unqualified applications.

Focus on what you're offering

Since you've just eliminated the need to list your demands, you have a lot of space to write about your company and what you can offer the candidate. Imagine it being a personal ad. You have to really sell the idea of working with you. Write about everything from your lunches together, your flexible hours, free coffee in the break room, etc. When you add these things together, the person reading the ad is going to imagine herself being there with you.

Market your company

Don't forget – job seekers are not the only ones reading your ads. Your rivals, customers and partners are probably reading them as well. Job ads are a really good place to see how a company is doing and how generous they can be. When you're writing the ad, make sure to imagine your biggest rival reading the ad. You're going to want to make them jealous, right?

Make sure you're not making stuff up!

So now you understand the concept of making your company sound like a great place to work. However, you have to be honest. Nothing is worse than a candidate that is disappointed right from the start of an interview. Don't say that you offer something that you don't. 
Be honest – but be sure to mention everything that makes your workplace a great place to work.

Be concise

Don't write too much. To be brutally honest, nobody wants to read about your company for more than two minutes, so make sure that your job ad isn't too long.