Split the sentence into two (or more) separate sentences. End each sentence with a full stop (a "period", in American English), and start each sentence with a capital letter.
Alternatively, if the two component sentences are related, such that the second sentence is dependent on the first sentence in some way, they can be joined in a valid way using a semi-colon (";") or a colon (":"). In this case, the second part does not begin with a capital letter.
For example, this is a run-on sentence:
Run-on sentences are bad English, people who write them should be ashamed of themselves.
This is really two sentences strung together. You could write them as such, with a full stop and a capital letter:
Run-on sentences are bad English. People who write them should be ashamed of themselves.
Alternatively, since the second sentence is really just a follow-up to the first, it makes sense to link them with a semi-colon:
Run-on sentences are bad English; people who write them should be ashamed of themselves.
It's really just 2 separate sentences. We went to my cousin's wedding. Over 300 people were invited.
Put .
Yes, it is, in all grammatical ways a sentence.
It is correct where you put it.
To fix the run-on sentence, you can separate it into two sentences: "Rajeet opened the window. He loved the smell of a rainstorm."
"How are you" is a correct sentence.
There are different ways to write this sentence. The best way to write it would be "What were you doing before this"?
Yes, this sentence is correct.
You are palpitating. This is a correct sentence.
With the exception of not capitalizing the 'y' at the start of the sentence, it is a correct sentence.
No, this sentence is not correct. It contains a hanging participle: 'Naming each picture' is not linked to the subject of the sentence. You could recast the sentence in various ways. Here is one example: 'Name each picture, and make a note of which names begin with the 'you' sound.'
That sentence is grammatically correct.