There are a million search engine optimization gurus out there and they all teach different things. Everyone tells you to worry about title tags, H1 tags, etc… What no one is telling you is that if you do everything in one whack you might not get the full SEO potential.
I did an experiment with a couple of sites. One was fully optimized, the other was partially optimized. Both were on the same topic and the domain names were identical (except for the extension). They were hosted on different servers in different datacenters with completely different IP addresses. I submitted both of them to the same exact sites, did the same exact off site SEO for both of them. A funny thing happened. They both ranked about the same in the initial rankings with the more optimized site 2 places up. Then once a week I started to optimize site 2 (the site that wasn’t optimized) with little changes like adding tags to images, adding more keywords, adding a title instead of a generic index title, etc…Over the course of about 2 months site 2 jumped up in the rankings about 17 places and site 1 jumped 5 places in the results for the same keywords.
A little note, these were static sites so there was no actual content changes during this time except for the small changes made to site 2. Also these results were on Google.
Since these were static sites, it looks like google was counting all the small optimization changes as new/fresh content, which in turn drove up the rankings.
It’s not always good to get everything done in one shot. The search engine spiders are smart and can tell when you make small changes to your site and in turn will reward you.
Of course it’s up to you how you do it. If you’re doing it yourself and don’t have to worry about a budget you can go the gradual approach. If someone else is doing the work and you have to pay for every job completed you might want to get everything done in one shot.