Below is a guide on how to Eco. Eco is when you sell and let your partner hold both lanes while you upgrade mines and send. It may sound easy but its harder than you think!
Step 1: It is always best to play to sell after 5 so plan your building with whatever builder you have accordingly. Build JUST ENOUGH or barely less than enough to hold the waves.
Step 2: If you have double rares, MAX THEM ASAP. Selling after 5 will allow you to finish maxing them for a wave 7 or 8 send. If you dont have double rares take farms and mana and max the farms. Also make sure to take gold mines BUT DONT UPGRADE THEM.
Step 3. After you have successfully maxed your double rares or farms, now you need to go mid! Only take manas, farms, or gold mines along the way. DO NOT TAKE METALS! They give you less for sends so it is not worth taking until you have middle.
Step 4: Once you have expanded also make sure to zap your acid lings on 6, female karaks on 10, glass lings on 12, and acid lings on 14 in your lane. Also try to zap steal the enemies boss on wave 9. sonic tanks on 13, and boss on wave 16. Make sure you also save zaps to help your lane partner hold. 2 zaps kill a rine and 5 zaps kill a pinky.
Step 5: Once you have captured mid, max any special mines you have grabbed. It is important that if you are low on metal or mana mines you do not use them to upgrade your special mines or mines you will only be using to send with. If you are low on metal and mana mines max early and stockpile those resources. After all what good is having all that income if you cant use it?
Step 6. ALWAYS make sure you save your gold and resources until you know your team is going to clear the wave. It is your job to upgrade the Mine Guard if your team leaks. DO NOT upgrade the MG as a source of income solely. It will put you rounds behind and is completely unnecessary. If you know you will be weak on a certain wave save a round in advance just in case you need to upgrade the MG.
Step 7: Once you max your special mines, max the mines you are going to use for building and try not to send with those resources. Only send with special resources or food.
Step 8: All of your mines should be maxed by 26/27 and you should start researching by wave 27. Your goal is to clear your lane by wave 30. Your income should also be around 200-300 by wave 30 depending on your mines.
Step 9: Build your army and crush your enemies!