You can save your searches as an email alert or RSS feed in most databases, including Scopus, Web of Science and PubMed. That means you'll get automatic notification about new articles which match your search.
Many databases also allow you to create Cited Article Alerts, so you can be notified when a particular paper is next cited. This is a good way to track who is citing you.
is a service providing access to tables of contents (ToCs) of over 19,000 scholarly journals, including open access journals from major academic publishers. You can search for journals by title or for articles by keywords, and set up alerts to receive contents of the latest issues of journals you have selected or the latest articles matching a keyword search.