If you can get a video of yourself, you could post that here and ask for comments.
I think what you'll benefit from is identifying the weakspots in your throw. I'm going to assume that you're reasonably healthy and not too old and that throwing over 280 is not unreasonable. If that's true, then once you identify the problems, you can work on correcting them.
As the last two folks said, it does take time, and making changes will make your game worse for a period of time. Making adjustments in your throwing style will throw off your timing as well as make your throw inconsistent as you learn the new process. Until the muscle memory kicks in, then you won't be able to perform the same action everytime at full speed, therefore, you'll either get it right at full speed, slow down and get it right or miss something entirely - any of which could mean throwing high/low or off to one side or another.
Once you're throwing your new process without thinking, you can focus on accuracy and nose down stuff and improve your aim.
It does take time though.
I've found that watching the videos in the throw analysis section helps a lot. You can pause the video at certain spots to see just what they're doing.
Some things to keep in mind when practicing:
1) Keep your chest over your thighs, not leaning back.
2) Keep your weight forward when you throw
3) Keep your grip tight enough so the disc doesn't wobble, but not so tight that you are flexing tightly and have no flexibility in your wrist/forearm
4) Make sure the disc rips out of your hand on release and that you're not letting go of it early.
5) Make sure that when you throw, you are following through the throw with as much speed as you put into the throw before release. Basically, it's like martial arts, don't punch the object, punch through it. When you throw, don't plan on your release being your end point, plan on about 90 degrees past your release being your slowdown/ end point.
6) Pivot on your heel or toe at release so you don't twist your knee.
7) Reach back as far as is comfortable and keeps you balanced. Recently somebody mentioned it helped to reach out away from their left side (straight out) and pull in towards their right chest for the throw. That would be a little like a triangle with the thin point being your release point/rip.
Make sure the nose/front of the disc is pointing a little below level when you release the disc. If the nose is up, then the disc will shoot into the sky and fall off to the left very quickly. The closer you can keep the nose to down, the more the disc will react the way it's supposed to (which is usually, rise, flatten, then fade).
9) Make sure if you cross-step that you are closing your hips and then driving them open again for power. The cross step is used to begin the rotation and is the source of the power of uncoiling.
10) Rotate with your shoulders as fast as you can. By this I mean use the larger muscles to pull the smaller ones. By rotating your shoulders quickly, it will help you pull the disc across your chest faster and result in more speed and distance.
11) Pull the disc through close to the right side of your chest. It doesn't appear to be as important to have it close all the way through, as long as it's close on the right side and out through the rip.
12) After the rip, make sure that your arm stays on the same plane as you were throwing. If it's a hyzer, your arm will being low and end high, if it's an anhyzer, it'll begin high, end low. A flat shot would be level all the way through. If you start level, but end down, you will torque the disc and turn it over (called off-axis torque).
13) Remember to step and throw as smoothly as you can. The more in control you are, the more likely you are to have a controlled and accurate shot. This doesn't mean be slow, it just means be in control and not jerky. At the discgolftv. website, Barry Schultz has a small video on this subject.
14) Look at what disc you're throwing and how it should react. If you're throwing under 300', I don't believe throwing a wraith, surge, pulse, etc. is going to help you much since they are ultra fast discs meant for players throwing maximum distance. I'd look to the discs like Gazelle, XL, XS, cheetah, etc. There are many great golfers here who can recommend some discs here that might benefit your current game (if you have a bunch of the high speed discs). This also goes for a specific shot. Don't throw a crush because it's a distance disc if you have a long hole with a narrow fairway. It might serve you better to throw a midrange or putter a couple times and par than shoot for a birdie with the wrong disc.
Just about all of the above is opinion - most gleaned from this site and the generous golfers who donate their time and advice.