I see you guys talking about Points and Miles, if I cared and focused I'm sure I'd get a better return with those. Personally I am all about cashback cards. In the past 10 years I've probably accrued 5k in cashback across numerous cards, all with 0% APR. Every 15-18 months I sign up for a new card offering 15-18months 0% APR with generally 1.5% cashback, and quarterly 5% promotions. I just hit 1 year on my discover, which matches the entirety of cashback earned in the first 12 months, netted $290. I intentionally put EVERYTHING I can on one active card, it super inflates what they think my spending power is. My previous card I worked on was an Amex Blue Cash, they were super aggressive with the limit increases. I make sub 100k, and by the time I was done working on that card I had a 20k limit. Technically at the moment my available line of credit across all my cards exceeds my income.
Once you accrue a few cards, every 6 months or so, ask for limit increases. Generally without issue, and without credit check you can snag $500-$1500 limit increases per card.
Other tricks, if he's buying anything that he can afford to buy outright with cash, DON'T. I just yelled at my Brother and his fiancee about this. They're both late 20's no credit cards, no student loans, basically no history. They got assistance from her dad to buy a car, so they bought it outright. They should have gotten a loan and paid it off aggressively. When your young the biggest thing that hurts a credit score is lack of data points. If you get one credit card great! You'll build up a score but it won't be stable, it will fluctuate until you have multiple accounts and/or a solid history to validate it all. I told my brother to get a cashback card, the very next month his score went up by 30pts.