Remember your publisher / agent are very busy. It is very easy for authors to act as if theirs is the only book that a publisher or agent is dealing with. Don't be offended by delays in responding to you. If it is an unusually long delay then a polite reminder will usually elicit a reply. I would however not let the fact that they are busy stop you from asking lots of questions.
Be active in helping market your book. You can certainly create a great web site, and your publisher will almost certainly support you in any PR activities, such as talks, seminars etc., that you have the energy to organise. Remember that your publisher (especially if they are a small publisher) probably has only a very modest PR budget for most of their titles, and as far as they are concerned your efforts are free. If my experience is anything to go by your publisher will be delighted by any efforts you make.
Respect your publisher's professionalism. Many authors belittle publishers for poorly packaging and publicising their books. Just remember they are the professionals at this not you! Most publishers welcome polite input from authors and will go out of their way to accommodate your preferences. When it comes to the final copy of the book’s contents you are the boss, but you ignore your publisher's suggestions at your peril. On all other matters your publisher is the boss but they will almost certainly welcome your constructive input.
Be professional yourself. In particular get your manuscript in on time. This will almost certainly involve a disciplined writing regime. You cannot wander through life waiting until the muse is in full flood. The muse takes best to discipline. If the worst happens and you are going to be late, let your publisher know in very good time. Also respond to your publisher's requests (reviewing editorial changes to the book, PR material, supplying photographs etc.) promptly.
Don't moan about the attention best selling authors (and their books) get. Pareto's Law, also known as the 80:20 rule, says that the publishing industry will get 80% of its income from 20% of its titles. My guess is that for books it is far more extreme than this and that 90% of the industry’s profits come from just 5% of the titles.