Welcome to FT.
I assume you are mainly look for award flight/ upgrade.
If you can share your location/ route people can help you better.
Depend on your spending (to meet minimum spending requirement for bonus miles/points) you should each sign up 4-6 new credit cards:
Depend on your airline preference:
1. UA (Chase UA, Chase Sapphire preferred, Chase Ink Plus)
2. DL (AMEX DL, AMEX MR, AMEX SPG)
3. US (USbank US, AMEX SPG)
4. AA (Citi AA, AMEX SPG)
5. WN/Southwest (Chase WN, Chase Sapphire preferred, Chase Ink Plus)