Ease your way into it.
Be it forum games, social relationships or whatever....part of perfectionism I think is often a combination of ambition and a lack of patience. When thinking of forum games, maybe you see a really good forum game done by someone with a lot of experience and you want to do the same thing and hit the ground running. And perhaps you're not really appreciating how long it took that person to get to where they are.
Or consider DMing a table top game. You run under a good, experienced GM and you're like 'Man, I want to run a game like that.' And you plot it all: the epic campaign, the 4' x 4' world map, a whole bestiary of your own.....and then you find you weren't prepared for the amount of work it really takes to be that good.
Or take social gatherings. You know someone that is fairly popular and seems to get along well with everyone and you're like "Man I wanna be like that." Without realizing that, while it may seem natural for them, chances are their social skills are finely honed by practice.
Or asking someone out. If you've never done it before, it's hard for most people to reign in their emotions and not look like a nervous idiot. But once you try it and actually experience what it's like, you observe how you did and how people react and apply that to the next time you try it. You know that your palms sweat or you stutter and you focus on keeping your hands in your pocket, or speaking slowly and calmly. (Personally, when I'm asking someone out I always cop to being nervous. It doesn't scream CONFIDENCE but it tends to, if nothing else, soften a rejection. In a way it's kind of a cop out because you're basically preemptively asking someone to sympathize with you. But most people worth dating will. And some even find it endearing.)
So break down your objective into smaller, component bits and try them out a little bit at a time. It's not 100% applicable to all situations but I think you can generalize it to a lot of things.
Most of all is: appreciate that failure is part of the learning process. In Meat Space, people are often their own harshest critics. You externalize that self-criticism to the rest of the world, believing everyone is noticing your failures and judging you. Which, to be fair, both are probably happening to some extent, but not to the degree your imagination believes. So I say this: joyously accept failure. Treat every failure as a chance to learn, and apply yourself to what you're weakest at. Don't view failure as a set back; view it as simply making a little less forward progress than an outright success. Framing everything you do as a learning process where there's no going backward gives you a psychological buffer against feeling bad about outcomes. Which in turn makes it easier to try things you know you might fail at initially. Be plucky about your failures! Even if you're faking it, that kind of thinking as a tendency to become real if you don't backslide into getting depressed, angry or frustrated with yourself.
What you might also consider asking yourself is, why is perfection so important to you? What goal does being perfect achieve? And if your answers keep taking you to some place outside yourself, I'd turn it around and examine it again. Because you're the one placing these burdens on yourself. (If I'm telling you what you're already aware of, sorry, just making sure you're putting the responsibility for the way you feel on the right person.)
If you can't find a worthwhile answer to "What does being perfect get me", or if the answer you find is one you're ashamed of (like "I want to be loved and admired") then perfection is actually your enemy.
Let me give you a total cheeseball example: The Matrix. Neo. The Jump Program. "Nobody ever makes it their first time." Well, guess what? Not even "The One" made his first jump. The Jump Program is really a statement about one thing: EGO. It's your ego that's making you afraid to fail. And it's your ego you need to learn to kill, so you can grow as a person.