Hello there, Ladies and Gents. The video below shows how to get the "Grand Opening" and "That Looks Classy" achievements in less than 15 minutes.
For the "Grand Opening" achievement, all that you need to do is finish the Introduction to the Diamond Dynasty mode. However, keep in mind that the settings you choose MAY be permanent, so if you have any interest in playing Diamond Dynasty beyond the achievement, take some care in your choices. I wasn't able to delete my team to try again, FWIW.
Load up the DD mode, and you will have a few tutorials and game experiences to play. You'll need to score a run with the bases loaded and nobody out and you'll also need to get 3 outs with your pitcher without allowing a run. You'll also have a bunch of menu tutorials with the game explaining the mode, rosters, buying and selling cards, etc. Just hit A through these, but pay attention if you are interested in playing more of the mode. Otherwise, the last introduction is for opening a Card Pack. All you have to do is open the card pack to get your achievement. IF you are interested in getting the "That Looks Classy" achievement as well and aren't going to play the mode any further, I recommend selling this card for the Stubs to make sure you can purchase the Bat Skin. Check the "That Looks Classy" achievement on here for my Guide to that.
If you have any questions, feel free to ask!