Like Ezn, I generally do not write or read shipping fics. Unlike Ezn, I am an Aromantic sex-repulsed Asexual. Though, there are expectations, like some of my WIPs, but even then, far from being the focus.
Before we start, a small tip in case you want to crosspost on AO3 (it is an archive, Wattpad's moody, so you may consider it solely to keep a back up of your fics, one available to readers, at that.)
AO3 has a tag section just for relationships. Romantic as well as platonic. And yes, there is a difference. These tags are the characters names, separated by either a / or a &.
/ is used for romantic and sexual relationships, while & is used for platonic and familial relationships.
A lot of folks don't know this, which is fucking annoying when you sort out romance fics.
I wish they would add a tag for hate relationships, like rivalries. Maybe use ! or #?
Rant over.
Let's start with something simple. You may alienate readers when you offhandedly mention a ship, especially a more controverse one or one canon-focused readers generally don't get behind. Unless it is somewhat plot relevant, try not to mention them just because they appeal to you.
Every part of your story should have a purpose.
On that note, plots are problems that want to be resolved. So make the couple suffer in some way. Mind you, the problem does not have endanger their relationship. Maybe the couple is a detective power couple that tries to solve very difficult cold case?
But if your plot is just romance, looks like you're not getting around this.
If the ship isn't the focus to begin with, please try to avoid that they push the actual plot into the background.
Now when writing these relationships, unless it is the plot that it is love on first sight, make sure that the love actually develops and has reasons to exist. Characters need chemistry. What do they have in common? How do they treat each other?
I can't give much advice on shipping, as I don't normally write it.