Working with a good instructor can be useful, but you can accomplish much on your own (and should even if you do work with one.)
i cant see my elbow and im know my stance changes sometime's because of my hip .
The counter in one of my bathrooms is close enough to table height to be useful for stroke training in front of the mirror. I take my shirt off to make sure I can see how the stick relates to my upper arm clearly without a sleeve getting in the way.
I aim the stick directly at itself in the mirror, taking care to find the stance and head position that allows the real stick and its mirror image to form a perfectly straight line. I can see where it is in relation to my eyes when it's lined up properly, and can also see if my upper arm is in line with the stick as well.
When I do this, it's very obvious if I don't stroke straight because it will cause an angle to form at the tip near the mirror since the sticks will move symmetrically to the side together. Doing this at various speeds gives lots of immediate visual feedback to fill in my mental model of what's happening during an otherwise difficult to see action.
and on a hard stroke i always swing out away from my side.
This may be caused by tucking your elbow in too much towards your body. It can create an angle between your upper arm and the line of the stick that moves your hand (and therefore the stick) to the outside when your bicep contracts. That can cause the tip to swipe to the left (for a RH player) and cause unwanted spin and deflection. You may have a complicated wrist movement that compensates for this at lower speeds but that doesn't work as well when the contraction away from the stick line passes a certain velocity.
Things are much simpler if you can use the mirror trick above to get the upper arm in line with the stick. The elbow joint only allows the forearm to swing in a single plane. By finding that plane in the mirror and aligning it with the movement of the cue, you can learn what it feels like to be in the ideal position.
Robert