- Hang in there. Once your players get the hang of their characters, combat will flow easier. The difference in the speed of combat from first and sixth level are like night and day. If you need something to help keep track of monster HP, powers they've used, or otherwise, there is a large market of DM apps that can actually control initiative for you. You could also try to ask your players to plan their move before their turn actually turns around.
- Start the adrenaline flowing. Nothing is as gripping as when their characters are actually in danger. I may be exaggerating a little, but if the party has proven that they can handle 5 kobolds, why not see if they can handle 8. Slowly scale your difficulty up to the point that the players are actually evenly matched. Design monsters to directly oppose some common tactics of your players to force them to think outside the box. Place environmental factors that both hinder the party if they aren't creative and are extremely helpful if they can make use of it. (pools of greek fire or oil are good for this.) Just make sure that the combat poses an actual threat. If one of your players is not knocked unconscious by the end of a boss fight, you may be going too soft. (warning, this isn't for everyone. Some players may dislike the extra threat from this in the same way that most people avoid skydiving even though others have done it before.
2.) It depends on what type of creative you are. I, personally, would be bored out of my mind with pretty much every premade campaign setting out there (with Dark Sun as a possible exception). Others prefer having the concrete rules about the mechanics of magic and the way society works to make a story around that. You say that most premade adventurere leave your players bored, so I recommend building your own story, and then the dungeons and combats to further the story.
- Building a world is a lot of work. Imagine typing up the entirety of the Forgotten Realms campaign setting without the book next to you, while listening to Nyan cat. It simply can't all be done in one sitting. Pace yourself. Once a week write a little something about your campaign world. For a basic template I suggest reading the worldbuilding articles on this very site. (look to your left)
- Give your world a twist. Why bother creating a world where all the rules in the book apply, when there are already so many of them? Perhaps the greatest power in the world stems from martial strength, not from magic, and those who practice magic are persecuted. Perhaps the world is long past the developmental point of Ebberon and have essentially coated the surface in magic-punk themed cities inhabited by Warforged. Perhaps the world is new, and your party and eight other people in a village nestled at the base of a mountain are all that exists in the known world. When you make something new for the players to play in, they can influence the world as much as you can, and players like that.
3.) Have you ever participated in a LARP or historical reenactment? As much as they are hated a good selection of people, the way they tell their story is unsurpassed. It's many times more engaging to be out in the world, experiencing the fatigue and exhaustion of traveling the wilderness, and actually fearing the "orc" that is chasing you with a massive wooden axe. Don't take this the wrong way, I'm not telling you to turn your game into a LARP. I'm telling you to follow that example and make your story so realistic and engaging that you weave a thick matrix of intricacy that your players believe that they aren't just watching a fantasy film unfold, they are part of it.
- Use the player's senses to your advantage. Play to their sense of smell, taste, touch, and hearing. Instead of saying;
"You are suddenly confronted by a large ogre, who angrily snarls as it attacks."
"You suddenly find yourselves gazing upon the coarse hairy leg of a massive green ogre. A trickle of spittle drips to the floor before you out of it's mouth as it releases a low snarl into the echoing cavern. Almost as soon as you see it, the great lumbering mass of toned green flesh begins to thunder toward you. It's charging!
By using sensory words like these, the players find it easier to visualize the ogre, instead of having to visualize it for themselves.
- On the topic of playing to their senses, why not actually play to their literal senses through the use of props. Why simply describe the contents of a letter when you can easily print out the contents onto brown recycled paper in a script font, and burn the edges to give the players an actual sheet of paper they can examine for clues? Use thematic music to set the tone of an area. It's a big fight, so go ahead and play some dramatic combat music from your favorite movies. A good selection of music can be found in the Official D&D Soundtrack, by Midnight Syndicate. Don't forget to use other senses too. Samples of leather or sandpaper can help a player feel the texture of a monster's skin. You can find plenty of halloween scented candles which appeal to the many odors found in a dungeon. Samples of food such as frozen Alaskan fish, portobello mushroom caps, or roasted pork can put a sense of taste to your game.
- And on a final note of getting your players involved, it's not a bad idea to let them put their ideas into the story. If you originally designed your game as an Indiana Jones'esque jungle explorer feel, and two of your players make criminals from the undercity, they're telling you they want a game based in a city full of crime, and it wouldn't be a bad idea to play to that instead, as long as your other players are okay with that. When your players are the axel that drives the wheel of the campaign instead of the pebble that gets picked up and pulled along with the wheel, then they are bound to be involved.