Look for projects or organizations to which you'd like to contribute. Visit their GitHub repository, read the instructions, and perform the search for first-timer issues. Working on as many issues as you can, either across projects or for a single project, is a good idea. Join their IRC channel (Gitter, Discord, Slack, and other similar services). When you're stuck, introduce yourself and ask for assistance. The links to the channels can be found on their GitHub pages. Start engaging in open source programs after you're comfortable contributing to open source.