In my opinion, being a 100% f2p user requires a certain amount of social interaction either through official discord or telegram channels or through joining a guild. There are guilds made for newer players some guilds that are more for vets might even let you join. Either way, a guild is a great way to meet people that are willing/able to delegate some cards to you for free. The Splinterlands community is full of amazing people however and joining a guild isn't the only way to success... simply ask if anybody can help you out in discord or telegram then sit back, grab a drink and get to know people. Don't feel discouraged if nobody helps out at first, it might just be that they prefer not to delegate cards till they know you better or see that you're active and wanting those wins ;)

edit:
renting Neutral cards can be more beneficial to you as they can be used in any battle (this way you aren't paying for cards that you can only use every few battles)