A few weeks ago, I was talking about baseball cards. Since then, I've learned a few things about how this hobby has changed since I last dealt with it in 1993.
Advice #1: If you're buying any more than a pack or two here and there, get a hobby box. A hobby box is different from a retail box; both contain 10-20 packs of cards, but the hobby boxes are pre-ordained to also contain special insert cards, typically 2 per box. These range from the mundane (slightly uncommon cards) to the rare (autographed cards, limited-run cards) to the valuable (cards containing pieces of bats, jerseys, gloves) to the priceless (a special foldout card holding pices of bats from Ruth, Mantle, DiMaggio...I saw a guy open a pack and get this in the store while I was looking around, he was talking about eBay and $500 bids.) Anyway, a hobby box typically costs more but you get more cards (often you can build your entire base set from the contents of one hobby box) plus the extras. You won't find hobby boxes in Wal-Mart or Sports Authority - you have to get them at specialty stores or online.
Advice #2: Before investing $50+ on a hobby box, first figure out which make and model of card you want to collect. A simple investment of $10 will get you single packs of 4-5 different brands, and then you can see which you like best. If I'd done this, I would now have complete sets from one 2005 brand, rather than six.
Advice #3: Get thick, screw-down card holders and a safe. All of our cards that list for more than $5 are secured in damage-proof plastic cases and stored in a small fireproof lockbox...just in case.