NBA Playgrounds

There isn't a way you can guarantee yourself a new player by opening packs, so you'll have to grind levels in order to recieve more packs.

Personally, I found this the fastest way to earn experince.

Exhibition Mode
Score: 10

All you need to do is hit 3 3-Pointers. The first will count as 4 points for being the first basket, the other two will net you 3. Rinse and repeat until you level up.

Use any players you want, but I'd reccomend playing using players with a high 3-Pointer rating, as well as against players with low block/steal ratings, in order for you to be able to score easier.

Alternatively, you can play through the tournaments to earn more packs, which have a higher chance of containing rare players.

The above solution is by far and away the best way to get in-game XP.

It should also be noted that you can get supplemental XP that will add up to saving you a lot of games over time.

When you get a duplicate player that is of bronze or silver level in a pack, the XP goes to that players progress bar. However, when you get a duplicate player that is of gold level, the XP gets put directly into your overall progress bar:

Legend +300 XP
Epic +200 XP
Regular +100 XP

So because you will end up playing so many games anyway, its good to start leveling up all your players to gold just because you will start getting free xp for duplicates. I personally started with all the legends and epics because they gave more xp.

*** REALLY IMPORTANT ***
If you level up while getting XP from duplicates in a pack opening, you will NOT get a new pack for that level. I tried it once, and haven't tried it since then because I didn't want to lose more progress. It's best to open packs pretty soon after you level up so you don't accidentally lose a pack by maxing out your XP bar early.