You absolutely need Rakdos Cacklers, Gravecrawlers, Diregraf Ghouls, etc... more low costed guys. Desecration Demon is more of a tempo card than an aggro card, seeing as he'll hardly ever attack. Rakdos is much too situational to be in a deck like this and so is Cryptborn Horror.
For an aggro deck, you want low costed guys that will always hit the table. You have way too many noncreature spells. Dreadbore and Bonfire are fine, but the rest are absolutely not. Fling is bad. Rakdos Return is awful. Underworld Connections and Mizzium Mortars belong in different decks.
Honestly, for what you're used to it looks like you'd just want to do a midrange or control list. Currently you have two choices: go with aggro, or go with a sort of controlly tempo thing.
For aggro, you want to have a bunch of little guys smacking their face for a bunch. I recommend cutting the Crucibles completely. You won't need them ever. Most of the time they'll sit there and you'll wish they tapped for colored mana. Once you finally get to pop one, your opponent will just chump block it. A 4/4 is not worth all of the investment. Get rid of all your noncreature spells other than Dreadbore and Bonfire, but cut the Bonfires to 3. Stick in some more burn, like Searing Spear and Brimstone Volley. Brimstone Volley will win you games in a deck like this. Add nearly every black or red one drop you can find. Stromkirk Noble [http://magiccards.info/query?q=stromkirk+noble&v=card&s=cname], Gravecrawler [http://magiccards.info/query?q=gravecrawler&v=card&s=cname], Diregraf Ghoul [http://magiccards.info/query?q=diregraf+ghoul&v=card&s=cname], and Rakdos Cackler [http://magiccards.info/query?q=rakdos+cackler&v=card&s=cname] all need to be 4x. Vexing Devil is fine for what he is, which is dealing four to their face for one mana. For everything that's not one mana, you want Blood Artists [http://magiccards.info/query?q=blood+artist&v=card&s=cname], Geralf's Messengers [http://magiccards.info/dka/en/63.html], and Falkenrath Aristocrats [http://magiccards.info/dka/en/138.html]. Those guys are fun to mix together. Honestly, a lot of people don't like him, but I love Hellrider [http://magiccards.info/query?q=hellrider&v=card&s=cname]. When you've got a team of little guys swinging with him, it's almost always a win. You can play around with the numbers yourself. I don't actually play this deck, but it's just a suggestion. Sideboards depend on your metagame. If a lot of people play zombies, side pillar [http://magiccards.info/query?q=pillar+of+flame&v=card&s=cname]. Tragic Slip [http://magiccards.info/query?q=tragic+slip&v=card&s=cname], Rakdos, Desecration Demons are decent situational cards that you wouldn't want mainboard. Sever the Bloodline [http://magiccards.info/query?q=sever+the+bloodline&v=card&s=cname] also helps pick off tokens as well as big guys that you want gone for good, but a bit heavy for mainboard. If this list sounds a lot like the ones from the StarCity links, that's because BR aggro is pretty much the same deck all around. Honestly, I didn't even look at their lists until just now to see what they had sideboarded and it was pretty much the same as what I said.
If you want to focus more on control, Desecration Demon is fine. You'd want Olivia [http://magiccards.info/query?q=olivia&v=card&s=cname] as well as Sever the Bloodline mainboarded... honestly, if you want to go control, Jund is how you do it. It's expensive, but running green is worth it for the Thragtusks [http://magiccards.info/query?q=thragtusk&v=card&s=cname], Huntmasters [http://magiccards.info/dka/en/140a.html], and just simply the ramp. If you do that, then you should be able to run Rakdos Return and Mizzium Mortars just fine. It gives you access to mana dudes and makes your Underworld Connections a whole lot better.
I hope my advice helped. I'm not that much on a standard player, either, but I know that right now, the cards I named have been proven to be pretty good. If you have any more questions, I'd be glad to answer them.
EDIT: And oh, not to be mean, but I think the other guy in the thread kind of gave you bad advice. This is a difficult situation because it was good advice for what you want to do, but I think what you want to do is bad o.o I don't know how to word this without sounding like a jerk, but trying to consistently play Lord of Riots and Rakdos Return will leave you burned because they're not that good. You'll spend all your time and energy focusing on adding way more lands and fixing to consistently cast them, but most of the time you'll end up flooding yourself and even when you do manage to drop one, your opponent will simply take the damage and then win next turn. When you run 25 (!!!) lands in an aggro deck, you're going to topdeck lands all the time when you really just need gas.
Aggro is about pounding their face as fast as possible. You want to win before they can set up board presence. Focus too hard on trying to drop big scary dudes, then you're playing a control deck. One drops are the key here, and the less one drops you have, the worse you'll end up being. Trust me, I played Tempered Steel when it was good. Aggro needs to win early. You shouldn't say "well what if they play..." because you're not going to let them play anything. All their energy will go to removing your guys rather than letting their deck work like it's supposed to. Aggro means aggressive, so you have to have that attitude.