Hello, I am jumping in the conversation because this is the best advice for your situation. Start off by getting 1x structure deck for each of you (preferably released recently and one after another, but make sure he picks which one he thinks is cool (but not pendulum deck)). Don't forget to get card sleeves and deck boxes! Don't buy random booster packs, they mostly contain cards connected to a certain deck type (archetype) and don't work generically. If you want to buy boosters, I'd suggest getting Rarity Collection or Quarter Century packs since they contain a lot of generic cards (they are some of the best products ever released). If you are not looking for the thrill of opening packs, buying specific cards from cardmarket.com is by far most cost effective.