When you first get your website developed you should find out exactly what level of service you are getting, if any for search engines. There are company's out there who specialise solely in SEO and SEM who may offer you greater advice in these matters but you need to weigh up whatever the costs may be. Your web developers may only include 6 months submission or similar package. Search engines are constantly changing their algorithms and you need to keep working on them. If you achieve a top listing you cannot leave it at that. Time will show you that results can change on a frequent basis.