Say yes by default

On social media or in real life, people invite you, suggest you to do things or ask for support.

You can find handfuls of very very good reasons to decline or ignore.

But take a minute or two to consider one thing: your current situation - where you live, what you do, who you live with, etc. - is the result of connexion you did not predicted.

Knowing that, maximizing interactions, give help, participate, join, pay interest too is key to move forward, make your life evolve. I can write dozen of posts on this. I recently read a book by the Dalai Lama and he agree with me. No better way to have a great life than to open arms. The more you give the more you have chances to get a lot in return. I don't think anybody can contest that.

I'm not naive, sometime I accepted thing I should't have accepted or connected with people I did not liked much but is it a catastrophy? Not at all. 
Does it worth filtering too much proposals? Honestly not, failure rate is extremely low.

Example: I took Vietnamese courses in a French association. At the end, I'm still low average in Vietnamese :p but I met amazing people, learned so much from them, took part to amazing event, learning how to cook for hundreds of people, how to setup a stage, how to be a security guard for Vietnamese Minister, visited Unesco headquarter in France, discovered how big performances are organized, discovered films, books, amazing dishes, companies people from the organization were working for (Officience, an amazing management less company), jobs (I did not know people were specialized in Airport architecture), NGOs etc. Cannot list everything.

Bonus: suggest!
Suggest lunches, parties, drinks, travels, buying a flat with friends (yes I did that recently - Catalan region interest me  a lot :p), creating an NGO, a company. To be transparent, I'm not good at suggesting and far better at sharing.
Indeed, I'm quite shy and afraid to disturb people, but I try.

If you're interested in this topic, read Never Eat AloneHow to Make Friends and Influence People and the Secret.

And if you want a practical exercise, do your life resume. List important moment of your life since birth. You'll see how luck, how not predicted connections shaped your life. 
I spent days doing it (and deleted afterward, too personal) and it learned me a lot.