I usually aim my stories at the kindergarten to middle grade age groups; exactly which one of those depends on the book in question. If at least some of your work is aimed at middle grade readers too, here are 8 tips on middle grade writing to get you started. They're not the best tips in the world, but they're a decent starting point for you to work from.
Speaking of writing tips... Here are 33 awesome tips for writing just about anything, which you may also find useful; especially if you're just starting out on your writing journey.
Also, here's a list of 10 surefire ways to nail a first draft. I disagree with most of them, but they're entertaining, so worth reading for that reason if nothing else. I do agree with number 10 though... When you've finnished your first draft - in fact, any long stretch of writing - it is nice to do something for the neglected partners, or other family members, who put up with being ignored, and often also yelled at, while you worked on your writing. I'm lucky in that my hubby considers my writing time to be time when he can play his video games without me bothering him, so we both win. But, even if you're as lucky as me, you should make a point of doing something nice for - and with - your family during writing breaks. The best option being to have some time set aside for both writing and family time every day, whenever possible; and this includes the furry or feathered family members you may have, since they need your time too. My rodent gang are pretty good about it, as long as I pay attention to them during writing breaks, and stop writing to go and comfort them if a storm rolls in and upsets them. That last is a shame, since I love both reading and writing during a storm, but I still go to them, and offer what comfort I can. My point is, you should always make time for other things as well as writing. The author of these 6 essential tips on time management for writers and bloggers obviously agrees with me; if the 6th tip is anything to go by, anyway.
Finally, here's how to Become a Goodreads Power User (and why you'd want to).