It’s not always possible to tell whether something is a good thing or a bad thing, you’re right.
Sometimes the author makes it clear by using a word like “unfortunately” or “regrettably”. If you post some TC sentences I can take a look with you to see if its possible to identify connotation or not.
I don’t have a particular question but I’m more interested in trying to generalise a way that I can use to say this sentence is good / bad.
One example of that would be what you suggested, if words like “unfortunately”, “regrettably” or any other negative words are there then we can say that the sentence is bad.
But is this a correct approach or since this is a very fundamental to TC (connotation), is there any conventional way to identify the connotation of a sentence.
Similar to what Ganesh said, for subtler sentences, it will still primarily be a vocab game. It’s not quite enough to know only the definition, you also need to be aware of how a word is used.
For example:
The fashion critic found the outfit garish.
The fashion critic found the outfit eye-catching.
In which sentence does the critic have a negative opinion of the outfit?