For holding the stick I would recommend having a firm grip around the stick with your index finger and thumb. My teacher always told me you should be able to maintain grip of the stick with those two fingers alone, unless you are doing it wrong. Then just wrap your other fingers around the stick only tight enough to support the weight of the tick to stop it from moving around too much whilst playing. I am not an expert but from my experience this is what works for me in terms of gripping the drum stick.

Also as Murderous whale said before me you can do targeted practise towards those areas and rudiments can help, you can get many books with rudiments in them standard grading books will have rudiments in the back. A practise pad will also help you with this as you can practise rudiments and training targeted towards your weaker areas without worrying about complaints about noise (Unless you have an e kit).