(these tips have not been in any particular order, incase you were wondering. the numbers don't really indicate any level of importance.)

try to keep some semblance of consistency with your characters, while still leaving wiggle room for them to grow.

as you write, your characters will change quite a bit. sometimes they grow, sometimes they tell you things about them that you hadn't noticed before... then sometimes they run rampant like a wildebeast on an acid trip in disneyworld. in these cases, you have to say "no, marysue, you cannot suddenly unleash an until-now secret karate mastery" or "no, man's man, you don't open up this story walking around in lacey underthings" or whatever may apply. as a writer you need to know when to let your characters explore themselves and when to chain them to a chair in the basement.

hyperbole aside, your readers need to have some attachment to your characters in order to care about them and what happens to them. if you're frequently rewriting characters (or redolling, as the case may be) to the point where characters are coming and going faster than your bowels on taco night, then you need to take a step back and contemplate what it is you're really trying to accomplish and how you want to tackle it.

there is of course a niche for that sort of stuff, and if you were to embrace it, you could have a lot of fun with it. the key is to not take your characters or story too seriously. you'd want to aim for silly, and toss the characters in without focusing too much on character development or backstory. the instant you start getting to know a character, that is when it becomes harder to get rid of them without losing the interest of your readers. then if you do it TOO frequently, your readers will be like "ugh why do i bother reading this when i know my favorite character will only be around for a couple of stories before everything changes?"

if you INSIST on having more serious stories, interesting personal histories, detailed characters, etc... then consider having an actual storyline to follow from beginning to end, and try to complete that before you cycle in new characters and a new story.

now keep in mind that when you are new to stories, things are going to change a lot. characters will grow and shift (let them! just keep them moderated) and maybe you're still figuring out what style(s) of doll you like. these things are all to be expected, and nobody can fault you for it. just keep in mind that if you want to pin down your characters and get people interested in your stories, you have to make some sort of effort towards some consistency.

my advice is to start out with carefree, unimportant stories. not only is it easier for your reader to get to know your characters (this is a tip all on its own, i'll elaborate some other time), but it's easier for you to get to know them, as well. don't get into some huge crazy storyline right off the bat that's gonna get derailed after a month when you suddenly decide that maybe the main character is actually more inclined to walk around in cargo shorts than frilly dresses, talks with a scottish accent, and suddenly is 20 years younger. the bonus is that easygoing stories will give you some good practice, as well as giving you time to build up a readership (this takes time).

tl;dr, if you can't keep your characters consistent, don't be surprised when you can't keep readers interested in them.