Please don't do the @twitter thing, we have a built-in quote function to indicate who you are talking to. Thanks.
Well, there are many things to know about soloing:
-You have like 50 skills, lots of talents, 3 different types of pet with abilities and talents : Know your class. And remember, not every modification comes in the patch notes!
Usually soloing requires you to use skills you'd never use in raid - summon, dismiss, taunt, dispel... It's the main reason I have absolutely no interest of abandoning clicking.
-There are many consumables out there - mostly potions that can come in handy in specific fights.
-Finally: learn the fight
1: Get an old version of Bigwigs/DBM (or both). It doesn't show everything, but it can help.
2: spend time on wowhead/wowpedia, read the commentaries, prepare yourself. You can also use youtube for timing.
3: test it. First of all, never spend more than 2 hours on a boss - it's worthless. You aren't extremely inventive during tries, for my part I never had the idea that got me the world first during tries. A good night sleep, thinking without concentrating on anything, and ideas can pop up.
Then, learn. What pierces deterrence? What can I taunt? What can I deflect with deterrence? What can I FD? What do I avoid if I take aggro? What can I despawn? What attacks won't hit my pet? What can I use at specific moments? (ex: the pet that cannot be controlled while Yogg-Saron's tentacle grips you, but that will attack it if you use kill command)
Getting a world first is, thinking, searching, getting ideas, trying, learning, making up new strategies while using the full extent of your class. That's why I managed many world firsts without ever setting foot in a Heroïc raid, keybinding, moving with my mouse or playing 2 hours a day. (It also helps I have only 1 raiding character - he gets the full extent of my play time).
EXAMPLE: Northrend beasts.
I considered them impossible - Gormok would despawn as soon as I FD'd, making pet switches impossible. But that was months ago.
Then I heard about a guy who had solo'd the other bosses. So I wondered "hey, why not try Northrend beasts?".
Then comes the "know your class bit": since Cataclysm, the pet Taunt was a 4-minutes CD 3-seconds lasting distracting shot: it didn't increase aggro, the boss would run back at you after 3 seconds. But I had also noticed about a month ago it now had a 1-minute cooldown. Maybe they had also made it a real taunt?
3 minutes and a wowhead comment reading later, I had my answer. I respecced my pets to give them taunt, then I went.
Gormok quickly fell - he was basically an unforgiving tank and spank at that point. I discovered I could also FD again - great.
Then came the twin jormungar. I quickly discovered that the snobolds were fire bombing me to an early grave, and had to go.
On my first try, Acidmaw never paralyzed me during the first static phase. So the question was, why? More testing, and it seemed that it had something to do with never taking aggro. It also appeared that dreadscale never applied burning bite to my pet.
Now, bosses have 2 kinds of capacities - the time-fixed ones, that they won't use, or that will have no effect, if they do not have any possible target (maexxna's cocoons, Kologarn's grip), and the CD - type ones, where they use the ability as soon as the CD is finished and they have a target (lich king's necrotic plague - or, in this case, burning bite).
So I tried 2 things: FDing to avoid paralytic spay - success, he would cast it without effect - and taunting + deterrence on acidmaw. It worked because burning bite is a CD - based attack, and pierces deterrence.
Of course, after wiping on Icehowl when he was at 9K hp, I realized the berserk timer was an issue - so I used this tactic every time possible to FD the least possible.
I didn't even think up a strategy for Icehowl, just pop cooldowns when he was vulnerable.
About that: use rapid fires and pet defense CDs intelligently, as to max out their effect. Macroing them in your shots isn't a good idea as far as difficult bosses are concerned. Readiness is a hell of a CD because it also readies your defensives CDs - I always pop FD before readiness to reduce my aggro before going wild with rapid fire.