Although it's not something I do, using Alaska could be a good choice for crediting your AA and DL flights. Keeps the mileage in one central location and there are good values to be had using their award chart.

The best microoptimization, by far, is to put yourself on a credit card signup schedule. There's a sweet spot to a quarterly schedule and, since you haven't been playing this game, there are plenty of high-mile offers floating around for you. You could consider putting into your calendar a FlyerTalk day, say every 3rd Friday, where you allocate a few hours to reading thru the open threads on the board, picking out one high value credit card, and signing up. Then spend the next 3 months using it as your everyday spending card to meet the signup minimum.

This slow of a schedule is almost guaranteed to have a positive impact on your credit score and should return over $500 in value per signup.