Compare strokes in ㅋ/ㄱ and ㅌ/ㄷ. For ㅍ/ㅂ, also compare where horizontal and vertical strokes sit. Do not use one universal rule of adding one pen stroke.
How to make the sound
Try each sound briefly. These are starting cues, not an automatic pronunciation judgement.
가 · 카 · 까
Practise one family first. 카 has a clearer puff; 까 starts more firmly. Compare both the contact point and the start of the sound.