The consult -- whether it's free or costs some kind of money -- is like a first date. Not much substantive happens; you and your potential new client are getting to know each other, to see if you really like each other and want to take this to the next (billable) level.
By and large, the consult is going to be free of substantive legal talk, except for the outline of the case. Here's what you can cover in a consult, and what you can save for later.
Most potential clients are actually kind of scared of lawyers. They've seen lawyer shows on TV and they come expecting to be bombarded with questions and yelling.
Your primary job at the consult is to make the client feel comfortable, to reassure him or her about confidentiality, so you can elicit some kind of coherent story. Whenever someone asks how to prepare for a consult with a lawyer, I always say: "Just tell a story." Get your potential client to avoid legal conclusions (which they so often think you want to hear): Just have them talk to you like you're a human being.
Fee disputes are among the top reasons why disgruntled clients file disciplinary actions against lawyers. It seems tacky -- and it is -- but it's necessary to bring up the subject of your fee up front. This also enables your potential client to make a smart decision about whether to stick with you or whether to go shopping for another lawyer. Always get fee agreements in writing and explain what words like "retainer" mean (because yes the client may nod, but he doesn't really know what a retainer is).
Not Any Legal Mumbo-Jumbo
Some disingenuous clients are really out for free or low-cost legal advice; they make the rounds to lawyers all over town in an attempt to piece together a legal strategy. But other times, offering substantive advice to a well meaning client at the initial consult could make them confused or get their hopes up. Really, you don't have all the facts yet, and you haven't done any research, so you're not in a place to say anything except "sounds like an interesting case" and do some research.
What the Client Wants
Don't forget that being a lawyer involves what the client wants. After all, someone has come to you for help. But the question is, how are you going to help? Some clients genuinely want a resolution; others want revenge, which (despite what you've read in the papers) the justice system doesn't provide. You'll need to really find out what remedy your client is seeking so you can decide to take the case (or not). A good consult should do just that for you.