If you want to tame without the dino gate trap method (specifically on the map The Island as that's where I tried it), make sure you know where all the waterfalls are. Then find a Giga and let it follow you to the waterfall. Make it fall down the water fall. You should be at the top of the waterfall and shoot narc arrows/whatever better option you have. Best to ride a flying creature with high stamina and health incase you get hit by it while you make the Giga follow you (it'll only follow when you land). Best waterfall to do this is the one next to the 2 snowy mountains, along that river up north/northwest ish, as it has both tall sides for it to get stuck in.