GPCs need to be introduced in systematic way.
Set 1 - s a t p
Set 2 - i n m d
Set 3 - g o c k
Set 4 - ck e u r
Set 5 - h b f ff l ll s ss
It is very important that you pronounce these phonemes clearly and correctly. If you don't, children may find it very difficult to blend them together.
When introducing GPCs, ensure you introduce them with the sounds, pictures, actions and lots of practise for forming the letter. You can form the letter with a finger in the air, on the palm of the hand, on the back of another child, on a rough surface like the floor. All these experiences will need to come before trying to write the letter on a whiteboard or piece of paper.