IPTC

You will soon realise that uploading a picture is only a part of the job of getting a picture into the different stock sites. You need to apply keywords, normally between 5 and 50. This can be tiresome but there is help. IPTC is a standard of storing the keywords in the pictures themselves. You can rightclick any picture, select Properties/Details and you will find the keywords under the label "tags". Enter them one by one, or paste in a bunch of them semicolonseparated (";"). Or use helper programs like IPTC, Microsoft Photo Info or why not Lighroom or Photoshop.

Warning! there are bugs:

Dreamstime: Sometimes you get the description but not the keywords, sometimes vice versa.
Shutterstock: Sometimes misses the IPTC-details completely.
Fotolia: Sorting. Duplicate keywords wont be removed.
Istockphoto: Entering picture data incorrectly (duplicate words in description or whatever), drops all your carefully entered data.

Here is a Photokeywording tool which uses keywords from pictures similar to yours.

Conclusion: Use Photokeywordingtool and ITPC as much as you can, it will soon save you hours of keywording your files if you use more than one microstoc agency. Another benefit is that you can use the keywords yourself when doing a search on your harddrive! Also, if your picture database breaks down, you will still have the keywords intact.