The rules you named are some I personally followed. One other extremely important thing is privacy when you want to crawl personal data like social networks. I

The rules you named are some I personally followed. One other extremely important thing is privacy when you want to crawl personal data like social networks. I personally avoid crawling data that inexperienced users might accidentally expose, like email adresses, phone numbers or their friends list. A good rule of thumb for social networks for me always was, that I only scrape the data that is visible when my bot is not logged in (also helps to not break the providers ToS). The most elegant way would be to ask the site provider if they allow scraping their website and which rules you should obey. I was surprised how open some providers were, but some don't even bother replying. If they don't reply, apply the rules you set and follow the obvious ones like not overloading their service etc.