1. You'll be tired looking for subbed old videos only to find it subbed by communities that no longer accepting new member. If that happened, just focus on comm that's still active. It's kinda upsetting being unable to watch subbed version of some hilarious gems. But, what can we do? Just deal with it. Some recent episodes are gems too. Just watch them.
2. You'll find out that some subbed videos you're looking for are subbed by active communities that require you to have certain minimal posts and comments. If your posts and comments are still insufficient, just take your time. Write stuffs in your blog. Maybe you can share your delicious cake recipe, review your favorite books, or just write your thoughts. Write comments in communities that have accepted you. By time, you'll have sufficient posts and comments to join their comm (it took months in my case). However, maybe you'll forget which community with which requirements, so you'll need to check their membership regulation. Again.
3. You can watch raw videos. It's easier to find recent-ish episodes than the old ones. If you don't understand Japanese, don't worry. Many of us are on the same boat. And many people are kind enough to livetweet Arashi shows in English. It helps us understand the show we watch in raw. In my case, after watching raw videos for two years, I began to enjoy it. My skill in using Google translate hass been rocketing :D
4. You'll be greedy and want to watch as many videos as possible. Just don't. Take your time. Else, you'll get tired and bored, maybe. Or, is it just me? I feel tired after downloading sooo many episodes of Shiyagare and VS Arashi and watching many episodes of VSA just for writing about their rules.
5. Say thank you. In another forum, it's considered spamming if you just comment "thank you". However, in most Arashi subbing communities in lj, they considered that kind of comments as appreciation. Lack of comments in their posts maybe will make them think "Is my subbing not good enough?" More comments, more motivation for them to sub. Except in dss.
6. You'll find many hardcore shippers. If that's your cup of tea, you're lucky. If not, just deal with it. Or avoid them. You choose.