Prominence takes into account your keyword use in headings, positioning of your keywords on the page and keyword use in links etc.
Ideally you should place your most important keywords in your headings or near the start of your web page. Ideal keyword density and prominence varies with each search engine. Generally a keyword density of 2-6 % is desirable. Prominence obviously should be as high as possible for your most important keyword, decreasing with keyword importance.
Keyword proximity refers to the closeness between two or more keywords. Usually, the closer the keywords are, the better.
1. How Keyword Density Affects Search Engine Rankings
2. How Keyword Density Affects Rankings In Search Engine
Using the example above, if someone searched for "search engine rankings," a web page containing the first sentence is more likely to rank higher than the second.The reason is because the keywords are placed closer together. This is assuming that everything else is equal, of course.