Anything in the world can be learned. Be it a skill, a trait, a subject - mastery in anything can be achieved as long as you choose to achieve it.
The first thing you need to do to learn anything is to be serious about it.
If you take something as a joke, there is no way in the world that you are going to get good at it. What happens is that if you take something as a joke, you never look at it without blinking your eyes. Also, the feelings that you relate to it, like it not being good enough make it even harder for you to succeed at it. If you won't think of something as good enough how will you ever put in an effort to get good at it?
So the best way that I see to try something new, something out of the usual or that doesn't match your perceived personality, is to do it silently.
Learn what you want to. Just don't announce it to the world before you even fully make up your mind for it. People's reactions, their feedbacks, suggestions, arguments, in my experience, just leave you astray. It leaves you in so much doubt, that you end up not choosing at all. So better to just keep your thoughts of trying something new to yourself.
If you need suggestions, ask for them indirectly, look for cues, instead of asking a direct question. That works way better. Again, this is according to my experience only.
Optimism is no different. It is just another skill that can be learned.
I wasn't always an optimistic person. I was the kind of person that always ran away from trying anything at all. New or old. I just wanted to be invisible and never seen by anyone ever. I was always thinking about the worst possibility which made me bitter towards life and people in general. Sadly, my family and friends had to take all my heat. Thankfully they didn't leave me stranded.
It was my need to be hopeful that I wanted to not be who I was and be better. Optimism was still beyond the horizon.
The first thing I did was to start noticing my reactions and thoughts. It was tiresome. Not one thought that crossed my mind was positive. I was an angry teenager. Why was I angry? I have no idea. I just was.
Once I started noticing my thoughts, I realized that I had the power to rewrite the narrative. No one had to know that in my mind, I had taken my words back and replaced them with new ones. I wasn't ready to do that out in the world yet. It would have hurt my image of an angry young girl.
As time passed, my reactions weren't just rewriting the words in my mind which by the way were already ut into the world. I was saying the positive rewritten words out into the world. I was saying positive things already. But it didn't happen in a day. It happened over years worth of time. Took me 3-5 years to get to a point where I had considerable results. This was a long time ago.
This wasn't the end. The learning never ends. I started consciously changing my views towards everything by focusing my attention on my thing and asking myself, what is the upside of it. There has to be something. I know I can find it. And then, no matter how long it took, I would find the upside of a situation.
Full confession - It wasn't easy. But I did find it.
Once I found the upside, the next question was, could I have reacted to that situation differently? Almost every time the answer was yes. So obviously, time once passed by doesn't return. But now that I knew that there was a different way to see that situation, a more optimistic way, the next time I was in an argument or a discussion, I reacted differently.
Again didn't happen in a day, but this was the start of me taking back reigns from my pre-programmed, always scared and always in survival mode, reactive brain to my in the moment, analytical and proactive brain.
One thing leads to the other. Make one right choice, the rest will follow.