A lot of consultants fear that they will give away too much in terms of advice during the pre-sales process. Here are some thoughts on how I’ve tried to keep sales processes on track:

1. As you are engaging the client prospect, try to envision the big picture for the solution approach to the prospect’s business problem. For example, you may see that the client needs to a) better articulate the problem statement and the key priorities (vision), b) decide on an approach (strategy), and c) execute on all the tactical operational things to carry out the strategy (tactics).
2. Communicate the big picture approach to the client.
3. Try to add some value by helping them to articulate and refine the problem statement and perhaps also add a detailed item or two that they should consider as part of the more detailed solution approach workstreams. Yes you might consider this giving something away, but you will need to be able to add value and show the client how you are thinking to be able to sell to them consulting services. The client prospect needs to be able to trust you.
4. Keep your pre-sales activities pretty tight. For example you might limit your pre-sales sessions to 2 to 3 meetings of 1–1.5 hours each. This will also help to provide some separation between planning and doing the work. If you are doing a good job selling your services, you should be able to tell within say the first 1-3 sessions whether you have a serious sales prospect and what the high-level requirements are to close the deal. Note you might be able to get to a high-level proposal or conceptual approach after the first 1–2 meetings.
5. For many deals, you should be making it clear to the prospect that you are trying to better understand the problem statement so that you can propose the right approach to solving the problem; you are not solving the problem right there as solving the problem will take days, weeks, or months of collaboration and work.

To recap, make sure that both parties understand the problem statement. Both parties should understand the approach and should appreciate that solving the problem will take both time and work. Offer some value to the client in advance of sale; this does not necessarily have to be much, but you need to establish credibility and trust. Finally, set some expectations on the cadence and timeline to get to a proposal or no-go decision.