Hmmm it depends
Do you prefer more light hearted dramas or dark ones? Romance or action? Or everything mixed? Comedy maybe?
If you are not feeling like getting out of your comfort zone, then you can try the ones you never touched but are the types you usually watch.
But if you're feeling adventurous, switch the type of dramas you usually watch. For example: if you like light, fluffy stories then watch a heavy plotted, dark drama.
Obviously it's very difficult to figure out, so you can also try to pick a drama you never heard of. It can be a pleasant surprise.