The lower levels are fairly tough. If you get delegated a few cards from other people that will make it easier. If a total beginner then I would suggest that you use a little of the 3000 credits that you get from purchasing the spell book to rent a few cards.
Each of the standard cards(free) you use will reduce your earnings. At the beginning it probably isn't that important.(others would disagree) I would suggest that you rent 1 or two level 1 summoners at .1dec/day. (Probably Kelya Frendul and Obsidian) and play a few matches. See what cards you like to use and rent those if they are around .1 dec/day. ECR Energy Capture Rate reduces about 1% per battle and regains 1% per hour. So roughly 24 battles per day to keep it from reducing your earning much. Write down what beats you and if the same mana requirement battle happen again use that lineup.
!PIZZA
Have Fun!