Here's my tips, from a candidate's view:
1. Avoid exaggeration and flowery language. In other words, try not to use the "You must be a dynamic self-starter with a powerful record of extreme success in the first rate strategy space with a global reputation for excellence" approach that so many ads contain. I get put off by these ads because I think "Oh man, they're gonna be trouble to work for... they want superman".
2. Specify the salary if possible. "Attractive salary" or "Competitive" is just too vague. It makes me think they don't really know what they want.
3. Be honest but emphasise what the job can do for the employee. Too many ads focus on what the employer wants (superman). What's in it for us? Tip: Offering a decent work life balance, if it is truly on offer, will make your ad stand head and shoulders above the rest.
4. Be realistic with what you can expect. Too many ads seem to be looking for people that basically don't exist. Nobody's gonna join a company for £80K/year and bring a £10M order book with them.
5. Give a telephone number, and answer it when they call.
6. Accept CVs. Do not insist on having us fill out an application form. We're busy people and simply can't be bothered.
7. Give dates about when you will make decisions. Ads that lack specificity just look speculative.
8. Don't ask for stuff you don't need. If you really do want somebody with "extensive experience of radically transforming corporations single-handedly whlist at the same time developing a £5M pipeline of new business" then fine. But if you're looking for a competent project manager or suchlike to roll out a few IT systems or something, then just say it.
9. Tell us in plain English what they will want from us.
10. Give the ad a 'human' voice. Avoid HR-speak.