Honestly, I get comic books to read them, share them with others, and get my kids into them. Some might be worth money, but we're talking about maybe $20 for a few comics, and pennies for others. I would never make back the money I spent. At the same time, I do want then to look brand new for as long as possible. So, focusing on someone who doesn't want to spend much, and keep them safe but accessible, here's what the comic store has taught me.
Bags (Sleeves)You need to get comic book bags. These are plastic (polypropylene) bags. You should get the Golden Age size. Comics today are more narrow than they used to be, so the Golden Age size doesn't give you a snug fit. But it does give you room to store actual graphic novels or comic books that are thicker than normal.
BoardsThe bags are good to keep dust off, but they won't give you support to hold the comic up. It would still flop around, and the spine could crack if the comic was on an uneven surface. So, along with a pack of 100 bags, you also need to buy a pack of 100 board backs.
My comic book store sells a bag and board for 20 cents per comic. Personally I buy a pack of 100 sleeves and 100 backs, since it's a bit cheaper (about $16 total) and lasts a while.
BoxesTo store comics, they have boxes made specifically to store comics. These are called long or short boxes. A long box is twice as long as a short box. I had a coupe short boxes starting out, and now have two long boxes. Most of them are 1/2 - 3/4 full, so I have a lot of room. A long box is really pretty big.
Again, these are pretty inexpensive. About $7 - $12 each. It's definitely worth picking up a small box. Even if you only get a few, you can box them up, put the lid on, and shelve them without worrying what might happen to the comics over time.
StorageThe recommendations I've read is to use a dry, warm environment. Essentially, keep them readily available to read, or at worst in a basement. Light will obviously fade them a bit. But I'm no where close to this being a problem since I'm so new. While a closet shelf would be best, I'm now using the floor in my office.
Have fun keeping the comics forever!