As a f2p, I find it hard to gain tokens without spending money on this game. So here's my method for f2p to gain some tokens.
1. Finish all daily mission
Try to finish all your daily missions to get that 10 tokens, it's not much but at least you can get 70 tokens a week.
2. Campaign
You can gain tokens by doing some unfinished campaign.
3. Raid
Raid is the best way to gain tokens. You can get up to 100+ tokens a week if you manage to beat raid at tier 5 or be in position 500 or or better. Tips : Heat is the best way in raid to get higher score. You can watch Jiyoon's vids for more tips.
4. Advertisement
If you think 2 tokens is nothing for watching an ads, try to watch 15 ads to in a day. In a week, you will have 210 tokens. Tips : Watch ads from pc, because from mobile it's much slower.
5. Clan Wins Rewards
Try to be in an active clan, where you clan could get 1k wins every season. It would guaranteed you to get 60 tokens a week.
6. Gold Portal/Special Portal
If you finished all 3 portal difficulties you will get 45 tokens, 60 if its a special portal.
I usually get around 500 tokens a week with Anonymous, by doing those methods. I hope this method helpful for people that struggling to gain tokens.
Also, sorry for my bad english