Nice first game. It's impressive especially at 13 in one week.
The best advice I can humbly give you is to try to find a simple but strong concept when you make a game, and then add your own little ideas that make your game original.
And I think one of the most important things is the juice. Add feedbacks and effects everywhere you can to make the game more pleasant (and it's not very difficult in pixel art).
Otherwise good job and continues to create games, it's a difficult job, but it's a wonderful job especially in a world where AAA games are more focused on profitability than player enjoyment !