Back in the early days of search engine optimization, it was pretty much a free-for-all because the search engines were not as good at determining the quality of a link. Even the introduction of PageRank, combined with anchor text as a signal, didn’t deter link spammers. As search engines have become more advanced, they have been able to expand the link-related signals they can use beyond raw numbers. Search engines can look at a number of factors, which can all combine and give them an indicator of quality. More to the point, they can tell whether the link is likely to be a genuine, editorially-given link, or a spammy link.
Diversity of link type means getting links from different types of domains. If all of your links are from web directories, that isn’t very diverse., and this is something very prevalent it business so be wary and be selective.
Relevent in terms of the words used in the link, use one keyword but try not to make it stuffed with them, that's also a potential problem.
Too many links..
If the link pointing to your website is among hundreds or thousands of other outgoing links on a single page, then chances are that it isn't as valuable. but on the whole, and there is also the probability that these types of pages are only created for links and do not have much real content on them, which is also a signal to Google. So when listing yourslef on directories consider this, potentially most directories are worthless in terms of links, and possibly even harmful.
One other factor here is that the quality of the other links on the page could affect you, look at it as living in a bad neighbourhood. You would prefer not to, so would your site.