It depends on the topic of the article, but for a how-to, I think I agree with the others when they say it should be somewhere around 50/50 text to image.
One of the things that is starting to get frustrating in FSM is articles that advertises a technique (let's say weathering, scratch building, casting, or whatever), but they show a lot of pictures of the technique completed, but little description of the step-by-step of how to do it. What little text there is seems to be bragging about how they used <insert brand> detail items.