A good method which works well for me and is very simple;
:Put a pan on medium heat,
:add a little veg oil (1 dsp),
:add your chicken pieces, dont overload the pan as the heat will be reduced juices will come out of the chicken and they will boil rather than fry.
:Move the pieces around the in the pan so they dont brown.
:once all the sides of the chicken have been fried a little add one small ladle full of base sauce.
:keep the heat up so the base reduces to a thick sauce and oil
:keep testing the chicken, by pressing down on the pieces.. if they seem "springy" then they are NOT cook inside.. if they seem firm and base sauce has been reduced then try breaking open the biggest piece and check inside.. the chicken doesnt have to be cooked all the way through if you are going to use it within 20 mins or so.. if it is to be used later then it must be cook all the way through before putting it in the fridge, the chicken can then be removed from the pan and left in a ceramic bowl and allowed to cool. this will relax the chicken pieces and will result in tender pieces in your final curry.
The important things to think about are; (1) if you use frozen pieces then cook them all the way through. (2) If your pieces are slightly raw inside then they will need to be cooked a little longer in the final dish than ones which are already cooked right through.(3) Dont leave pieces out in the warm too long, always put the (cooked) pieces in the fridge after 20 mins?.(4) dont add your chicken to your curry if the sauce hasnt been reduced, add it nearer the end. This will stop the pieces getting stringy.
Good luck!!