This is specifically for the Digiland tablets that Best Buy has been selling for rather cheap (as low as $40 on the 7 inch and $70 on the 10 inch).
I'm a tablet/Android newbie, frustrated by how limited the amount of space for apps was on Best Buy's Digiland tablets, and it seems like a lot of people are. After a little bit of searching and combining a few different sources, I managed to resolve the issue using a Windows PC (sorry Mac users! :( ), and thought I'd put it all together in one place (just parroting what I found, really).
I did this on a Digiland 10.1, but I imagine the 7-inch version would work the same. And, of course, DO THIS AT YOUR OWN RISK! I take no responsibility for what you decide to do with the words of an admitted Android newbie. :)
There are three parts total, and you'll need a micro SD card, probably of at least 2 GB for it to be worth it (I'm using a 32 GB card). You'll probably want something that's faster too (look for a "Class 10" card). You'll also need to download two free programs to your PC, and one free one to your Android.
MiniTool Partition Wizard: http://download.cnet.com/MiniTool-Partition-Wizard-Free/3000-2094_4-10962200.html
Link2SD from the Google Play store.
Part 1: Root your Digiland
1) On the tablet, go to Settings > Developer Options, and checked the box marked USB debugging.
(If Developer options isn't there:
Go to Settings > About and then click Build number seven times to unlock them. It sounds weird, but it works!)
3) Connected the Digiland to your computer.
iRoot will automatically look for drivers. It's a long process, and took a good ten or so minutes for me.
4) Once drivers are found, iRoot will display a button that says "Root". Click it, and iRoot will run another long process. During this time, the table may reboot.
Part 2: Partition your memory card
(In the examples below, I used a 1 GB micro SD card, because my 32 GB card is already in use. :) )
In this step, you're going to be creating two partitions on your micro SD card (basically, splitting it into two parts). You'll need to decide how much memory to use, and this is up to you and the card you're using. Some sources say to only leave 1-4 GB for the second partition and that the first partition needs to be bigger than the second (so, for example, if you had an 8 GB card, you could split it 6 GB and 2 GB). I personally split my 32 GB card into 18GB for the first partition and 12 GB for the second partition (where the Android apps will go), and it seems to work fine.
1) Put the micro SD into the computer (you'll probably need an adapter, but most micro SD cards come with one) and fire up MiniTool Partition Wizard.
2) Find the listing for the SD card in the MiniTool Partition Wizard. Be absolutely sure it's the memory card you want to use, because your other hard drives will be listed as well! It will also erase everything on it, so back it up first!
3) Right click on it and select "Delete".
4) Right click on it and select "Create". Choose "Primary" and set it to FAT 32 (for media files; readable by Windows), then choose the memory size for it depending on what you decided to go with/what card you're using.
5) Right click on the second "Unallocated' portion, click "Yes" on the pop-up, and set it to "Primary" and EXT4 (some sources said EXT2, but only EXT4 worked with my Digiland). Set the memory to the remaining space on the card for this.
6) Click "Apply" in the upper-left corner and it will begin to format the card. This process may take ten or fifteen minutes.
Part 3: Set up Link2SD
1) Open Link2SD on your Digiland.
2) Put in the SD card. A window will pop up in Link2SD with several options. Select EXT4.
3) Link2SD should briefly flash a message that says something like "mount script created", and then it should ask you to reboot the tablet. Go ahead and click "reboot".
4) After rebooting, open Link2SD, click on the three dots in the upper-right corner, and then click Settings. In the Settings menu, check "Auto Link" beneath the Auto Link heading.
5) If you have existing apps on the tablet, they won't be automatically linked to the SD card. You'll need to click on each app within Link2SD and then click the "Link to SD card" button.
You're all set. All applications should now install to the SD card!
As of this point, I have nearly 5 GB of applications on the SD card. I have dozens of them now operational on my Digiland, including some games that are particularly big (Order and Chaos Online clocks in at nearly 2 GB in itself).
Apps will allegedly run slower off of the SD card than off the internal memory. Even so, I can run fairly graphic heavy games (see below for a few screenshots; you'll just have to trust me that they were a solid framerate!) without much trouble. I don't know if that's because it's a relatively fast card (Class 10), or if the slowdown was exaggerated. In my mind, being able to install way more apps is worth the speed trade off, but your mileage may vary if you actually see a difference.
You can always move particularly intensive or important applications to the internal memory, and leave lesser-used stuff on the SD card.
Sometimes the games on the SD card leave "obb" files on the internal memory, some pretty big. When you're looking at an app in Link2SD, it will show you if there's an obb file, and give you an option to "Link to SD card". I've been doing that, but I don't know the potential issues that might arise from that.