One of the most important elements to building an online marketing strategy around SEO is empathy for your audience. Once you grasp what your target market is looking for, you can more effectively reach and keep those users. Google and Bing have moved far beyond algorithms that positively reward a keyword appearing multiple times in the URL string. Don’t hurt your chances of earning a click (which CAN impact your rankings) by overdoing keyword matching/repetition in your URLs. If you sign up to become a member for a site, you'll get a link in your profile. Well, not every site. Some sites will allow quality links in your profile, while others won't. Some are in the middle, such as Twitter, which gives nofollow links (links that don't pass link juice). Speed is a ranking factor for desktop and a very important usability factor for mobile. Google is very serious about page loading times on mobile and that’s why they have introduced and pushing for the implementation of accelerated mobile pages. If you are getting links from a site that has high PageRank with many other links pointing to it then those links will boost your site's popularity.
If you're not sure, get a freelance SEO consultant to help you.