In all honesty, there’s not much you can do to prepare for the Wrath of the Lich King Expansion except for saving up your gold and most importantly - tradeskill materials . Why Tradeskill materials? Well I expect that Blizzard would be raising the profession caps (note: I am not sure about this, just a speculation), this means that many people would need tradeskill materials to powerlevel their professions as most characters have 2 non-gathering professions (eg. Jewelcrafting and Engineering). So what I suggest you do is stock up some high-end materials:
- Cloths for Tailoring and First Aid
- Ores for Blacksmith, Jewelcrafting and Engineering
- Dusts/Shards for Enchanting
- Skins for Leatherworking
- And most importantly, Primals for basically all the professions
Most professions even at level 375 have a few useful yellow recipes which I bet will be very useful when leveling above the current profession level cap. Having stocked up in some of the most important materials gives you an advantage with the rest of your server in creating new patterns and items allowing you to dominate the markets 