Even if you think you know about the keywords that your customers use to find companies like yours, always, always do the keyword research! We've had several customers lately who came to us with their keyword lists and insisted that they already know how customers find them. Then, we did the research and found many more valuable, and higher traffic producing terms. So, always start with a clean slate and always, always do the keyword research!
Only optimize for keywords you can compete on! A common mistake is to pick the hottest keywords regardless of budget.
If you're on a limited budget, pick some second-tier keywords that don't appear to be as competitive. It's better to rank #1 for a lower-traffic term than it is to rank 25 for the top term in your industry.