I was wondering how do I specifically say "it was the first thing that came to mind" as in this instance I have to describe an image (about badminton) but am wary of the different meanings and translations of 'something'.
C'est la première chose qui me soit venue à l'esprit.
Strictly speaking, I believe that the presence of the phrase « la première » requires the use of the past subjunctive « soit venue » instead of « est venue ». Then again, both might work.
Also, I would personally use the present tense « est » instead of « était », since the past tense is used in the part « soit venue ». I’d rather avoid using the past tense twice.
Apart from the debatable question of which tense is to be used, I'm a bit surprised to see all answers propose this kind of translation:
C'[est|était] la première chose qui me [soit|est|était] venue à l'esprit.
Maybe (as a French native speaker) I have a bad comprehension of the implicit sense the original sentence may bring in English, but the first translation that came into my mind (oh! What a coincidence) is rather:
C'[est|était] la première chose qui [vienne|vient|venait] à l'esprit.
In other words the original sentence might talk about what comes to the mind of anybody, rather than to the speaker itself.
"C'était la première chose qui m'est venue en tête". Or you could also say it like "C'était la première chose qui m'est venue à l'esprit".
So 'Something' means 'quelque chose' in French. 'Thing' means 'chose' in French as well. In French just like in English, you would not want to use 'thing' to describe a specific object or action.