First, we shall talk about 'they're', 'their', and 'there'.
'they're' is short for 'they are'. Remember that, and you shouldn't make any mistakes concerning it.
'their' is a term used to describe something belonging to two or more people, such as, "That is their dog." or "Those shoes are theirs."
'there' is a term commonly mixed up with 'they're'. By not 'compressing' 'they're', you should be able to differentiate between the two easily.
Next up is 'your' and 'you're'.
'your' is a term used to describe something in your possession, such as, "Your shoes are dirty." or "Your pet monkey is ignoring you."
'you're' is short for 'you are'. Remember that, and you shouldn't make any mistakes concerning it.
Finally is 'it's' and 'its'.
'it's' is short for 'it is'. Remember that, and you shouldn't make any mistakes concerning it.
'its' is used to describe something in a non-human's possession, such as, "Its shoes are dirty." or "Its fur is matted with blood." If you don't know which goes where, substitute 'its' with 'it is'. If the sentence doesn't make sense, it's 'its'.
Most grammar mistakes are made because of not 'lengthening' the word. If you do that, you should be much better with grammar. Thanks for reading.