The predictions you should make from personality assessments and the like about yourself should be fairly isomorphic to those you'd make about other people upon learning the same data. For instance, if I know someone with a particular Myers-Briggs result, and then I learn that another person has the same one, I will expect a certain level of similarity between the two people on that basis; I should make the same guess if I discover that I have the same Myers-Briggs score as someone I know. Tests themselves often supply predictions, although they're very vague and may require some precisification.

I'll use the love language idea because that's so easy to implement. There's five of them, and while I think there's a test available, it probably doesn't improve much on self-diagnosis. So, I look at the descriptions of the languages, conclude that I'm a "quality time" person because that fits best, and read what it says to expect from myself: Hmm, are distractions, postponed dates, or the failure to listen especially hurtful to me? And then I take off from there. (If I can't easily answer the question or refine my self-model relative to the provided suggestion, I assume that the description is accurate.)

Tips on getting friends/family to provide feedback: I find musing aloud about myself in an obviously tentative manner to be fairly useful at eliciting some domain-specific input. Some of my friends I can ask point-blank, although it helps to ask about specific situations ("Do you think I'm just tired?" "Was I over the line back there?") rather than general traits that feel more judgmental to discuss ("Am I a jerk?" "Do I use people?"). When you communicate in text and keep logs, you can send people pastes of entire conversations (when this is permissible to your original interlocutor) and ask what your consultant thinks of that. If you do not remember some event, or are willing to pretend not to remember the event, then you can get whoever was with you at the time to recount it from their perspective - this process will automatically paint what you did during the event in the light of outside scrutiny.