Info on 2 phones

I got new iPhone & gave my previous iPhone to my husband. Transferred info from SIM to new phone, but put SIM back into old iPhone since my husband had not had a mobile phone previously. How do I keep from all info now being added & deleted on both phones when it’s done on either one? Was advised maybe just changing Apple ID on one, but don’t want to now lose info on either… just want to keep future info on each info separate.