I know the original post is a few months old, but FWIW here's a cynical view from my own personal experience of building -- yours may differ (but it might not):
* Trust nobody. Your builder (if you are going with a prime contractor) will be the nicest person you ever met until the project starts. You may very well hate him by the end, so keep the relationship businesslike and not pally.
* Make sure there is a detailed written-down specification of what the builder is doing, drawn up by an architect or engineer. By the end of the project there will be little (and not so little) items such as what condition the site will be left in -- spreading topsoil, finished pathways or hardcore for same etc. You want this all to have been covered in the initial spec, because things will be forgotten otherwise.
* Ask if you don't understand a term. An example might be "prime cost" which is supposed to be an approximate cost for something that cannot be fully costed up front. In practice it is the builder giving a stupidly low estimate to make his total price look better than his competitors. He will charge you anything he likes in the end, so challenge all assumptions about cost, especially PCs.
* Keep a constant eye on progress. If you can't be on site every day, or most days, then this type of project may not be for you. Something that has been done wrong may not be fixable if you leave it too late.
* If you're dealing with a prime contractor, remember not all subbies are equally reliable. If you see a problem with plumbing, or carpentry, or electrics, keep a closer eye on those aspects until the end. At least one of the specialisms will probably be done by someone not fit to be employed, so make sure you don't pay for their mistakes.
* Be absolutely clear that you will not be paying for anything that you didn't agree up front. Say this explicitly -- do not leave it to chance just because it seems obvious to you. Your builder will add "extras" to each staged payment, and this will get worse over time if you don't nip it in the bud. Tell him loud and clear that anything he does on his own initiative will be at his cost, and that you must agree any changes in writing.
* Do not bow to pressure to finish quickly at the end of the process. Typically that is when YOU will be choosing wall and floor finishings, kitchens, bathrooms etc. Make sure you have done your research in advance, but if you're not ready, don't let the builder do things like putting in skirting before your floors are down, or bully you into making snap decisions.
* When "snagging" do not just do a cursory visual inspection. This is extremely important. You'll probably assume nobody would intentionally leave a job unfinished, or even untested, whereas in fact the chances of everything being in perfect working order are practically nil. So: test every electrical socket; test every tap including plumbing for washing machine, dishwasher etc. Do this with hot water available to make sure everything is plumbed the right way round. Check that plugholes and drains drain, and that overflows work. Douse grouted seals with water -- bath and shower tray edges, sink surrounds etc. (and leave time to spot any soakage through plaster or walls). Run your heating system for at least a day or two (regardless of whether this was also done during the building's "drying out" period). Hose down roofs and make sure your guttering is correctly angled to drain properly. Make a detailed inspection of all plasterwork, varnish and paintwork, etc. Be creative in thinking up other things to test. Do not be pressured into snagging in a single two or three hour session. Record everything photographically and in writing, and make sure you specify in detail what and how you expect things to be put right. You will be living with the results for a long time.
* Make sure you get certificates and guarantees where appropriate -- e.g. to prove that your heating system was not only installed but commissioned according to manufacturer's spec. Ask for proof that your builder has paid any specialist subcontractors, or speak to them yourself, rather than find later that someone won't come back to service their installations.
I'm sure there's more, but that's what springs to mind. (I may have mentally blotted other other horrors).
"Prediction is very difficult, especially about the future" – Niels Bohr