When making survival make, please remember to not follow minecraft mobs types, because they are too easy to avoid, making the game look like creative mode. 

Add a similar mob to silverfish, which can spawn on the place where block was mined, or when you smelt or craft using stone. 

Remember to not allow players to find a way to breath underwater, for example using doors which can't be waterlogged.

When a mob cannot fight back, because of block placements (imagine mob grinders), the mob should go away to not get cheesed.

You should take less damage if mob is behind you. 

Allow some mobs to smell you through walls.

yay!