If you're just starting up and need an idea how you can maximize your start up try reading the wall of texts below.
When starting up and your goal is play to earn you'll need to buy the spell book($10 or PHP500 + taxes depending on MOP)
After buying a spellbook pwede ka na mag earn ng DEC every win in ranked matches. The higher the win streak and rank the bigger the amount.
For starters:
I would recommend you to invest atleast $3- $5 worth of dec or credits just to rent out 1 team para simula palang mag winstreak ka na up to bronze 1 and mag accumulate ka na ng dec. Sa bronze 1 kasi nag start ang rules ng battles and dun ka magkakaroon ng lose if your team is not available.
I highly recommend this strat since simula palang mama maximize mo na ang capture rate mo.
(Avoid renting cards that are on cooldown kasi di nyo siya magagamit agad. You'll see it when you're choosing to which cards to rent nasa bandang right side ng price my little. Ircle parang timer if highlighted it means on cd siya if not then it's ok)
(If wala naman extra para sa $3-5 you can grind them dec and pag na accumulate mo na ung amount needed to rent the cards you can proceed)
- RENT DEPENDING ON YOUR CAPACITY
For example you only have 300 dec, rent for a day and grind it till you earn double the amount that you use for renting the cards. (make sure to maximize your capture rate and don't let it step down below 50%)
If meron kang malaking amount ng dec then rent for the whole season but make sure to grind your account.
Personally I would start by choosing a team whether it's fire, water, light, death, dragon or earth I'll start renting normal to epic cards for 15 days kasi sila ung mababa ung presyo at abot kaya for 15days. Then I'll rent legendaries for 7days and accumulate 3 times the amount I used within those 7 days before the legendaries expire. Then continue to rent again for 7 days and repeat. By the end of season I can say the you have either quadrupled your starting dec or maybe more depending on how you manage your capture rate.
(Normally if your just starting I would advice to compose a team or 2 till you get a good grasp of the game mechanics then continue on your own discretion)
Sa mga aspiring champion ranks naman, I learned this the hard way. Based on my experience if you want to reach champion rank you have to have atleast 7k dec(base to sa price na nagamit ko last season pero mukhang kulang na siya ngayon since sobrang mahal na ng mga cards for rent)
Minimum of 7k dec I managed to reach champion rank with 3 teams rented all max level monsters and summoners. It's quite the number for me since I never invested anything here just the spellbook so yung ginastos ko yung 7k na un medyo hesi.. since all of that was from grinding for several days. But I can say it's def worth it sa dami ng loot box na makukuha mo once mag end ang season.
Personal Advice:
If you got into the game just because you want to earn and don't want to invest more than the spellbook you can do so with just renting but don't expect to earn much kasi limited yung capabilites in renting since you'll depend on the dec that you're earning. Most likely you'll have a slow progress in ranks since dun mo din kukunin ung ipang rerent mo next time aside from your profit.