I give you my best thought. If I started over right here right now playing splinterlands I will buy just one card wich is DJINN OSHANNUS. That one card combined with playable water deck will give you a lot of winning streak. You can read my post if you want to know more about DJINN OSHANNUS.
It's all my personal opinion because everyone is different. But if you buy DJINN OSHANNUS at current price which is very cheap you will increase your chances in winning battle.
Good luck my friend.