The first thing to try is always hiding the tablet in some delicious smelly food, broken into smaller pieces if necessary. If they simply won't swallow a pill here's our handy technique:
Tempt your cat in with a treat, then stroke their head with your left hand before gently but firmly holding either side of their cheeks between thumb and finger. Leaning their head back slightly causes their mouth to open so you can use your right hand to insert the tablet right to the back of their tongue. Let their mouth close and gently rub their throat to make sure they swallow.