He Who Must Not Be Named
Names have great power. They can inspire hope, fear, excitement-or they can be a distraction and make your readers say "Who was that again?" It's easy to name stuff, but names don't cement characters and locations in a reader's mind; descriptions and relevance do. At the same time, obviously name important stuff, like your main character. Unless they're a fairy, and by revealing their name you give the readers ultimate power over them. Do not name them then.
Whose line is it, anyway?
If you took everything out of your story aside from the dialogue, you should still be able to tell what character is saying what line. Your characters should have unique voices to match their unique personalities.
He said, she said
Quipped, snarled, scoffed, sniveled, groveled, grunted, grumbled, exclaimed, whispered, whimpered, whined, breathed, boasted, hissed, hollered, murmured, postulated. Are you bored yet? "Said" gets boring after a while, but so does a constant barrage of different placeholders for "said". That's not to say never use them. I use them. I love them. But go for balance and, where possible, just let the characters speak for themselves.
Repetition isn't fun to read. Unless it's done for emphasis repetition isn't fun to read. Even when it's done for emphasis repetition sometimes isn't fun to read.
Read the Atmosphere
Or write the atmosphere, I guess? Atmosphere is essential to establishing a solid setting, and can be a real boon to plot and character development. Establish atmosphere through description, character reactions, and dialogue, and when/if you want to change the atmosphere, make sure it's done smoothly. For instance, I knew from the get-go I wanted a dark, bleak atmosphere for Children of Icarus--it's a story about kids trapped in a death labyrinth, after all-so I was sure to avoid adding impromptu BBQ parties with monster kebabs.
This story's a highway, I wanna write it all night long
When embarking on your story road-trip, please be wary of plot holes. If you get stuck in one you may be spinning your wheels for hours. You may not even notice the hole without the aid of a backseat editor. Let them tow you out. Just remember: however long it takes to fix and however frustrating it may be, a plot hole's not the end of the road.
Try not to let your character be a Peter Pan. By all means, create wily, immature tricksters, but be aware that character growth should occur. Just as life leaves us changed, plot should leave characters changed, be it permanent or temporary. Character development was a huge focus for me in Children of Icarus; the protagonist starts out physically and emotionally weak, faces traumatic events, and must either rise to the occasion or break completely--or maybe she does something else entirely?
Burn Your Bridges
Rather than bridging relevant plot-points with irrelevant filler (such as a carriage ride from Point A to Point B wherein nothing happens) try a page break instead, or start a new chapter. Chapters are there to enable your inner pyromaniac.
You must be this tall...
If you're a younger writer with immediate publishing aspirations, there are tons of people who are going to tell you you're "too young". So long as you're not telling yourself that, then you're not too young.
Your story may at times seem flawless. When you're with it, you're invisible to the rest of the world and literary criticism can't hurt you or your story. This results in you going in circles-or rings, if you will-with your story. It never evolves, never improves, and likely will never be published. Be open to suggest, be willing to make changes, and try not to coddle your story. Finding a beta-reader named Sam may also help.
As I am a writer and not a mathematician, I wrote eleven writing tips when I was only supposed to write ten. So the Ultimate Writing Tip-11. Wasps are the Worst--will have to wait for another time. Also, if you want to put me to the test and see if I follow these tips myself, feel free to check out Children of Icarus (spoiler: I ignore at least one tip from this list).