I've started practising and I wonder what are the stoic thoughts on sharing your achievements with friends/anyone.
I used to share all my achievements with everyone and it was causing some troubles, people tend to get jealous etc.
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Your attitude, is of paramount importance if you want to avoid the "negative" effects of "sharing your achievements" (or anything else). You will never go wrong with an attitude of humility, even to the point of giving the credit for your achievement to somebody else! You should avoid "coming across" as a conceited person, or one that feels superior to others, because of the achievements. But, most of all, avoid false humility!
No. The way I see it, this behaviour is not stoic.
Take a look at the Manual of Epictetus - The Enchiridion.
And let silence be the general rule, or let only what is necessary be said, and in few words. And rarely, and when the occasion calls, we shall say something; but about none of the common subjects, not about gladiators, nor horse-races, nor about athletes, nor about eating or drinking, which are the usual subjects; and especially not about men, as blaming them or praising them, or comparing them.
Epictetus sees stoics as people of few words. Talking about your "achievements" is certainly not something you have to talk about, especially if you are the one to bring it up. The way you speak about your actions in the question and comments gives me the impression that you talk a lot.
I would consider talking about "achievements" to fall in the category of what Epictetus called "common" or "usual" subjects.
But an even better fit would be the last part:
[...] and especially not about men, as blaming them or praising them, or comparing them.
That's exactly what you are doing.
In this section he speaks about the way you are supposed to spread or show your ideas and ideals.
On no occasion call yourself a philosopher, and do not speak much among the uninstructed about theorems (philosophical rules, precepts); but do that which follows from them.
This is a bit farther away from you but I think it might be a good lesson on how modesty is viewed in stoicism.
You act rather than talk and if someone asks you about something you do not start to show off or even worse actively search these situations out by bringing it up.
I think at some point I read a stoic text that directly mentionened bragging but I do not remember where I read it. It wasn't positive of it, that is for sure but I didn't want to rely on this if I could not source it. I will add it afterwards if I will ever come across it again.