This is a tad long, but I hope it helps.
Don't be afraid to make mistakes or re-writes. Write and keep writing, even if it doesn't make any sense at the moment. But also, don't be afraid to take a step back and chop away. There's going to be times where you reach a point in the work where you feel you absolutely have to keep something, but don't let that stop you. Many times, it's the paragraphs/sections you want to keep that have to go or be shaped for the greater/deeper good of the overall work. There will also be times that what you thought was the purpose/plot of the story will change. Don't be afraid to let your work speak to you as you go along. Treat the work as if it's a living entity. If it wants to go in another direction, let it guide you.
Save frequently so you can go back and forth and experiment. Roam in the world that's being created. Once you finish one draft/version, consider changing point of view. Ask yourself what-if questions in regards to plot, characters, mood, etc. As you go along, ask yourself who/what is this character. Do the same for your secondary characters, treat them as if they're your best friend. Who are they, what are their motivations, how do they fit/go against the plot/other characters. Is a character round or flat? Why are they, and how does it go with/against the greater theme of the work or society? Don't be afraid to LOVE your antagonist, they have the potential to be your deepest character. A great antagonist is someone a reader can hate and find something to love about them, especially when it works with the theme of your work. The journal suggestions and other ideas that you've received are spot on.
In the process, read others' works and ask yourself questions about them, and keep reading, even stuff that you normally wouldn't give a chance (Edgar Huntly, Or, Memoirs of a Sleepwalker is a great pick.) What is it about the characters that draws you in/away from the work? What do you like about them/what would you do differently? What do you draw from a particular author, their style, their ways of description/imagery/grammar/emotion-tone use. How does a particular author differentiate from other authors/yourself? How would you build a particular scene? Why did a scene(s) stand out to you? How would/could you say something in your own words? Study what authors have done in the past and are doing currently. I would even suggest studying the writers behind the works if you can. Think about how their lives are/have been translated into their works. What do they weave from their own lives into their works, and what are their struggles? How do they convey them consciously or subconsciously into their works? Ask yourself these questions, but of course, enjoy the work for what it is, or could be.
Form-wise, for dialogue, identify who's speaking right away. For instance:
"Dialogue," zay said, "is great when the person speaking is identified immediately."
Vary it up of course, but this is a rule that I've been taught which helps keep your fiction and dialogue tags clean. Also, depending on the mood you want to portray, it can pay dividends.
Also observe the world around you. Speech patterns, walking patterns, how people convey themselves in various emotional states. For your settings, ask yourself what emotions you feel when you see/feel a scene in your mind. When sunlight filters through the window, is it warm despite it being cold outside? On a cloudy day, are the clouds struggling to pierce the building they hang over, or are they merely looming lazily. Or is there hope, as sunlight struggles to but ultimately breaks through. Compare what your character sees/feels to your real-life experiences.
Another read I suggest is Annie Dillard's The Writer's Life. It's excellent for a beginning writer or for someone who has been at it for a while. It gets you inside the head of a writer, gives you direction, encouragement, and helps you in those inevitable times when you'll feel frustrated and when you feel all alone as a writer.
Don't fret over the bad days. Days you want to write but can't seem to get a sentence right, much less a paragraph. You'll read something and ask yourself how a particular work/author was published. There will be days when you're ready to throw it all away and ask yourself why you write. Don't give up. It's in those times that you're on the brink of growing. I hope and pray this helps.