Regularly FTP Upload Your Site
Search engines love fresh content so introducing a server side dynamic content section that puts up fresh content every time a bot visits is good.
This still leaves the actual file unmodified though.
The Lastmod Date
Most web servers suport the lastmod date which tells a search engine spider the last time a file was updated. If the data file was last updated wasn't very recently then a search engine will not do a full crawl of the page and condsider it dated information which it already has a copy of.
Save and Upload
By simply opening your files in note pad and clicking save you are changing the last modified date. Right click on the file and check properties before and after to confirm this.
So if you go through all of your files without changing anything but saving the file and then upload them your web server will report the lastmod date as very recent which will catch the search engines attention. This will cause the search engine spider to do a more thorough crawl of your site.
Couple this with an automated content section and you have one effective automated way of increasing indexing frequency.
The SEO Files Recomends
Regularly save and upload your files and include a random content section to increasing indexing frequency.