There's no fixed order in which to send these documents. Sometimes I send the T&C before producing a quotation, sometimes with the quotation, and sometimes after the quotation has been agreed in principle. Email is a great way of initially sending these documents. If the content is acceptable, I then send paper copies for the client to sign.
The Quotation
Clients typically want fixed-price quotations for specified deliverables. Sometimes, that's not possible, and you will have to provide an estimate. Fine, as long as you and the client are clear about this.
Before producing the quotation, find out as much as possible about what will be documented. For example, I send clients a checklist that asks questions about the product and the users. I then include this information in the quotation.
In the quotation itself, specify these things:
Basis of the quotation or tender. For example, I state that it's based on the software that I've seen and the number of screens specified by the client. If more functionality is added later, or if there turn out to be many more screens than expected, there is a good case for requesting extra payment.
Background to the work. Include a few paragraphs that give a high-level overview of the product and what it's used for. This helps to ensure that you are on the right track; the client can easily see if there are any fundamental misunderstandings.
User experience. This is very useful. Even if a full user analysis is not possible, at least you can specify what they are expected to know or not know.
Peripherals and ancillaries. If the subject is part of a system or process, one IASIG member specifies the inclusion of references to other equipment systems which are necessary to give a complete picture of the subject he is documenting.
Deliverables. Itemise each deliverable. For example, for a small project you might just specify a price for the final deliverable. On the other hand, for a larger project you could specify a draft as being a deliverable. Some IASIG members suggest that you can even ask for money before starting a project.
Sometimes you can give clients a set of options for the deliverables. For example, if cost is an issue, give two options: the cost for a full and comprehensive user guide and the cost for a brief getting started guide. This gives the client some choice, and in any case will certainly make the client think about what is needed.
Format / specification. If there is no formal specification, one IASIG member defines things such as the overall layout (e.g. A4, single-sided) or format (e.g. Microsoft Word, HTML, PDF). Alternatively, you could present this information as part of the deliverables.
Validity period. State for how long the quotation is valid.
Problems with the Quotation
Sometimes, there isn't sufficient information from which to produce a quotation. This is likely to happen with larger projects. One solution is to offer the client a fixed price scoping project in which you spend a few days or weeks investigating the project. Another alternative is to work for a daily or weekly rate, but clients aren't likely to be keen on that, since they want to know for how long they will be engaging you.