- If I were there, things would be better now.
- If I had been there, things would be better now.
Which sentence is correct one?
Are both correct?
Do they mean the same?
Taking just the first phrase, either would be possible depending on what context you wanted to use the sentence in.
were there - in the present; he is not there but imagining the situation. Colloquially, nowadays you may also hear ‘If I was there’. Personally I dislike it but it has become so common as to be accepted other than in situations where strict grammar rules need to be followed. For more information google ‘subjunctive mood’
had been there - in the past
However, because the second phrase in the sentence clearly indicates that whatever he is talking about took place in the past (because he is comparing a past event and its effect on the present) then only (2) is correct.