Check that any work undertaken needs planning permission with your local councils planning department.

Write a Work Specification, giving clear details of the exact work that you wish to have carried out, including who responsible for clearing any rubbish and ‘making good' after the work is done.

Choose a builder that has previous experience and specialises in the work that you want done.

Check if the builder is a member of any of the professional bodies such as the Federation of Master Builders.

Get several quotes detailing exactly what work needs to be done and the price you need to pay including any extras. Make sure that all the quotes reflect the same work specification including site clearance, material supply etc.
If one of the quotes is widely different (either higher or lower) from the other two, try to find out why. It may not reflect the standard of workmanship, a builder with little work may put in a low quote just to keep working while a busy builder who does not really need the work may put in a high quote.

Ask for 2-3 references and follow them up. A good builder will not mind showing off their previous work. Its often a good idea to get a reference from the builders current job as well as for work done similar to what you need.

Avoid paying any money upfront and ask for a fully itemised receipt. Ask for details of the required payments. For all but small jobs, the builder may ask for payments at specific stages of the work. The payments should reflect the amount of work already completed.
If the builders require any money before they arrive on site, think very hard before handing it over - advance payments may be required where custom made materials need to be purchased.

If the job is a big one, ask what guarantees are offered. If it is a new house, you will need NHBC (in UK) or similar warranty cover. Ask the builders about public liability insurance, they should have cover to protect you and the general public in the event of an accident. Ask the builder to undertake a small job first to see what quality and service they offer.

Be wary of traders who call unexpectedly and offer their services. Make sure you check out their credentials and references first.

• The work to be carried out.
• When the work is to commence and be completed.
• The cost of the work and when/how it is to be paid. If the job is being funded by a loan, which will be released to you at fixed stages of the work, make sure that the builder understands this and the actual points at which funds will be released.
• Try to include a 'retention'; part of the price which will be paid (say) 1 month after completion of the work subject to satisfaction. This will allow you to uncover small 'defects' in the work after the builder have left the site and gives the builder an incentive to fix them quickly
• Any 'local agreements' - such as use of washing/toilet facilities, disposal of waste etc.

When the work has started, you will need to 'work' with the builder. Record the progress of the work; keep a note of all instructions you give the builder and payments you make. You should feel free to ask the builders what they are doing - any two people may interpret a work specification in different ways; so make sure that they are doing what you want.