it depends on the hair you have...if you have any split ends i would suggest getting the cut off because hair wot grow fast at all with them. after you get it trimmed, condition it and try not to blow-dry/ straiten it- as heat will cause more split ends.
Also, your hair grows longer in the summer because the sun provides it with more nutrients. For example my hair grew a little over four inches just in the summer, but it only grows about two during the winter. So the season can affect it too!
When washing ur hair massage in the conditioner. Also at night leave ur hair loose and not tied up. They say 1/2 inch a month but doesn't mean that it's average. Try not to blow dry. Also USE SULFATE FREE shampoos and conditioners n products. Any harsh chemicals to ur hair damages the hair and really takes longer to grow. I use L'Oreal EverSleek!! :)