All experienced bloggers know this.... but for the newbies out there. Remember to have a photo for each and every post you do. And put it right up the top of the post.
If you don't have photos of your own, google one - but be careful - if you are a blog with commercial content - like ads or you are trying to sell something - then you must only publish photos that are for common use or that you have permission to use. There are a lot of common use photos out there.
If you get a photo off Google Images, remember to save it to your hard drive before posting it. If you don't, you will find it disappears from your blog after a while.
If you are using your own photos, try to get them as good quality as you can.... here I am in the glasshouse throwing stones since my photos leave a lot to be desired still - particularly when I am snapping food at night - artificial light does you no real favours.
Do try and put captions on as many of your photos as you can - apparently it helps search engines find you, too.
Good luck with your images.