1.) Don't hold back when you find out that you're pregnant -- go after and interview for the jobs you want!
2.) You are not obligated to disclose your status until they make the offer you are looking for. Disclosing your status too soon could automatically put you in a rejection situation. Once they've fallen in love with you as an employee, they will start thinking "How can we make this work?" instead of "Never mind."
3.) It is important to remember that they are making the commitment to you and have chosen you as the best candidate because you have exhibited the necessary qualities and skills.
4.) When the job offer is made, make your start date and maternity leave part of the negotiation.
5.) Keep in mind the nature of the job (i.e. hours, travel obligations, etc.) Be open to the fact that they may not be able to accommodate your needs because of certain requirements and expectations of the job or company.
6.) If a negotiation cannot be reached, decline politely and remind them again of how qualified you are for the job.