Kia ora tatou! This week I source from the Ngata Dictionary to get a better understanding of 'For'. I too continue making the mistake of using 'Mo' everywhere. Hopefully this episode is helpful.

Ngata Dictionary pg. 180

for hai Fetch some apples for our lunch. Tīkina he āporo hai tina ma tātau.

for mo We left for Gisborne. Ka wehe atu mātau mo Tūranga.

for mo These fishhooks are for catching snapper. mo te hopu tamure ēnei matau.

for mo The child was very forward for her age. He tino mātau te kōhine mo tōna pakeke.

for mo Get ready for the concert. Me takatū mo te konohete.

for mo We walked for a long time. Ka haere mātau mo tētahi wā roa.

for mo He gave me a new book for the old one. Ka hōmai e ia he pukapuka hou mo te mea tahito.

for i To seek for happiness. Ki te rapa i te hari.

for me Let's go for a walk. me haere tātau ki te hīkoi.

for mo They were punished for speaking Maori. I whiua rātau mo te kōrero Maori.

for mo Are you for us, or against us. mo mātau koe, kaore rānei.

for kua She swam to the island for there were no canoes. I kauhoe a ia ki te motu kua kore kē hoki he waka.

for utu She gave me five dollars for finding her purse. Nāna ahau i utu i te rima tāra mo te kitenga i tana pāhi moni.

for mo That's for upsetting your little brother. He utu tērā mo te whakatangi i to taina.

not for long kaore i roa The child cried, but not for long. Ka tangi te tamaiti, engari kaore i roa.