Rule 1: Get excited about your position.
Before you sell a candidate on a position, sell yourself on it. A candidate will never be more enthusiastic about the position than you are. Spend some time finding out what the positives are in the position and the type of candidate that would match best for it.
Rule 2: Make sure you have a good match.
If you're working too hard to close a candidate then take a step back and ask if this is a good match.
If you feel it's not a good match, spend your time working to find a better one.
If you feel it is a good match, work to express this to the candidate.
If you're not sure if it's a good match, you haven't qualified the candidate or position well enough, work to re-qualify.
Rule 3: Pre-Close a candidate. There should be open, direct communication before an offer is presented. You should have a clear idea of what the candidate is willing to accept. Example: According to our previous conversations, if we were able to get you an offer at the responsibilities, title and compensation we discussed are you ready to accept?
If yes, you've done your job.
If no, get things nailed down before you go any further. Candidates should have a paper offer letter after they verbally accept and before they give notice to their current employer, they may also want to clarify terms of employment/benefits. There are 2 other reasons candidates may ask for written offer letters:
1)They ask for the offer letter to buy time while shopping around for other offers.
2)They are using the offer letter as leverage to get a raise from their current employer.
If you feel a candidate is asking for one of the less savory reasons, then you should hold off until the candidate is ready. A job offer is active, and can not be made to another candidate, until a candidate accepts, declines, or it expires. Putting an offer out with little or no guarantee of acceptance can severely impact your time to fill the vacancy.