I’ve managed to avoid the common newbie mistake of just entering information without checking the source and I’ve always included at least rudimentary citations. Unfortunately, as I’ve become more experienced, I’ve learned that these rudimentary citations are often not good enough. Basically, your source citation should include enough information to allow you to retrace your steps in your research, and allow another researcher to retrace your steps and verify your information.
There are several guides for citing sources. The ‘gold standard’ is Elizabeth Shown Mills ‘Evidence Explained’. This 885-page book gives examples for citing almost any type of source you can imagine, and if it isn’t in there, you can always visit the Facebook page and ask for advice. To be honest, though, I consider this overkill for anyone who is not a professional genealogist preparing reports for a client or a genealogist who hopes to publish her research professionally some day. It is complicated and cumbersome, and somewhat intimidating, meaning I am less likely to cite more sources if I try to use this as a guide. I always feel like I am creating them the wrong way, to why bother?!
Other genealogists prefer a more simplified approach to source citation. Ben Sayer’s Practical Citation uses this approach. You can also use other approaches including the Chicago style method of citation, the MLA style, etc. Your genealogy software will probably have some citation templates built in. Mine does, but I still find it necessary to modify the template to meet my needs. You may also choose to use a companion app that organizes your sources outside of your genealogy database, like Evidentia, or even a spreadsheet. The St. Louis Genealogical Society has a handout with templates for the most commonly used types of sources. These follow the Evidence Explained model of citing sources.
Unless you plan to publish professionally, my advice is to just do whatever works for YOU, but make sure you do SOMETHING to cite your sources! Using a birthdate for your grandma’s sister because your grandma told you so is fine, as long as you include a citation saying the information came from a conversation with Grandma and giving an approximate date for the conversation. The important thing is that when someone asks you how you know grandma was born in 1937, you can tell them where you found that information. They can then decide if this is a reliable source or if they need to do more digging!