So there's a lot of guides out there on how to RP on Dreamwidth. These are all cool. They give you an idea of the attitude you should have, what kind of lingo gets thrown around, and essentially lay out steps on how not to be a dick. So this isn't one of those. Instead, this is a guide to all those cool technical things you can do to streamline your RPing. Usually in the form of addons! Now, this is written primarily for Firefox or Chrome users. There may be counterparts to some of these addons for other browsers. If so, comment and let me know!
Account ManagingIf you're like me, you have a lot of Dreamwidth journals. For me, I have my personal one, my four or five in-game RP accounts, my additional characters I play on memes, and a few journals related to modding my game. Logging back and forth between them would be a pain! Especially if they use different passwords, which they should! Fortunately, you don't have to do this. LJ Login and LJ Juggler streamline this by giving you a handy drop down list of your accounts.
LJ Account Juggler for Google ChromeContrary to the name, it works for Dreamwidth too! Also Insanejournal and a few other sites. This handy little tool created a drop down list of journals that you've added. You can switch back and forth, which means you no longer have to do all your tags for one character before switching. Handy? Very.
LJ Login for Mozilla FirefoxThis is similar to LJ Juggler, but in some ways is more effective. It can get a little more complicated, but the nice thing is that it makes use of any saved account/passwords you've already set up with Firefox. Like LJ Juggler, it's a must have if you play more than one character!
Don't Lose Your Tags!No RPer should be without
Lazarus Form Recovery! This useful addon will save what's inside your text boxes. This is a big deal because thanks to the way Dreamwidth is set up, you can lose an entire reply just by clicking away from your current page. Or you could lose it if you have an internet hiccup. Or just so many ways to lose it! But Lazarus will save these form responses so you never have to scream and rewrite a tag again.
Lazarus for ChromeLazarus for FirefoxDon't know how to use it? Just follow the instructions on the linked websites!
Note: Useful as it is, Lazarus can be a memory hog and is prone to crashing. So if you have a slow computer, it may not be the addon for you.
Tag FilteringThis part doesn't require an addon, but it is written primarily for Gmail. A lot of these concepts work for Yahoo or Hotmail or other email clients, so if you can follow along with what's going on, you should be able to follow along. First let me show you what exactly you get out of it. Check out my inbox, which luckily is full of tags, because I'm writing this instead of answering them:

I use this email address for RPing and for personal emails and all sorts of things. So having tags in my main inbox is a no no! On the left side, you'll notice the "DW" label. I have this set up for all of my tags to flow into there. There are sub-labels for the characters I play as well. That way when I'm in my "DW" label, it's conveniently color and character-coded. At a glance I can look at this and be able to say, "Well golly, I sure am neglecting Ling, aren't I?"
So let's walk through how to set this up. The first thing you want to do is go to Dreamwidth's account management:
(link). The third row will show your email address. So click the Change link.

As the example says above, you're going to want to add some identifier to your email address. You can use your journal name, so for instance, I might user 'username+deadpoet@gmail.com'. My personal preference is doing it by character name. The important thing is just to stay consistent for your own sake. In my example, we'll be using 'username+spike@gmail.com'.
Note: Make sure you head to your inbox and make sure you verify your new email address ASAP! Otherwise you won't get new tags!
Creating a central tagging labelNow let's head over to gmail. I'll trust you know how to login to your own email, so go and do that. We're going to go through two type of filters. The first we want to make is a 'DW' label. This will put all your Dreamwidth tags into this folder! If you don't mind them being in your inbox, you can skip this step.
In gmail, go to your setting. This can be found by clicking the gear on the top right, just above your messages. As someone who once was confounded by trying to find the settings in Gmail after one of their updates, I'll go ahead and include a picture!

Now in the settings, go to the "Filters" tab. Find the "Create a new filter" link. This will cause a box to show up.

This filter is easy. We want it to be "From"
dw_null@dreamwidth.org. That means whenever you receive an email from that sender (which is where all dreamwidth tags come from), gmail is going to flag it. Click "Continue >>" and the box will transition to the second screen.
Now that gmail has identified these emails, now we're going to give it some instructions. If you don't want them in your inbox, then you'll want to check "Skip the Inbox". Also check "Apply the label". Select "New Label..." from the drop down list and name it "DW". Whether or not you want to apply filter to existing tags is up to you. If your inbox only contains unanswered tags, then definitely select it. But if you're looking to build an efficient and organized inbox, then I'd hold back on checking it.
Creating Character Filter/LabelsNOW we move on to doing it character by character. Remember how I had you change your email address? Well now it's going to pay off.
Once again, go into your settings and into your Filters tab. Select Create a new filter.

Here we want to put your email address in "To". So for this example, the character Spike, I will type username+spike@gmail.com. Now click Continue >> for the next screen, where we will give gmail instruction on what to do. Again, select "Skip the Inbox" if you don't want your tags in your main inbox. Now select "Apply the Label" and in the drop down list, pick "New Label"

In the first text area, put your character's name. If you created a "DW" label in the previous step, then find that in the drop down menu. Now click the Create button and then click "Create Filter". Bam! You're done. Now you can test this out. Try replying to one of your character's posts with an alternate journal. Watch the magic!
Now, if you want to color code them, that's easy. Just head over to the list of labels on your left side, under the inbox. You'll see a small box appear with an arrow in it. Click that box and a new drop down menu will appear. From there, just pick the color you want!

There you are. All done! Repeat those last two steps for every character you have and you're good to go!