Often when I am starting a new wip, I feel that I have to go back and revisit all the things that I have learnt. Twyla Tharp called it polishing around the clock face. You work on one thing and then other things get a bit dusty, so you have to work on that. Without exercising various skills, it is impossible to stay in peak fitness.
A big lesson for me when I was first writing was learning to trust my characters and their conflicts. Also not being too nice to my characters and resolving issues too quickly. Without conflict the tension goes down to zero. Another sign can be adding lots of subplots and extra characters. Or having them interact quite often with secondary characters rather than with their other protagonist.
It is why authors spend a long time getting to know their characters and discovering what makes them tick. So you resolve one problem, andthat leads to another problem, esculating the tension between the characters. Making the stakes greater. Asking yourself -- how can I make this worse? How can I really turn the screws? Can I trust my characters to actually have deep seated problems before their character arc is complete? What are their feelings -- beginning, middle and end? Why will they be willing to give their love? What are the goals, motivations and conflicts?
And I have to remind myself of this every time I write. My natural inclination is to be kind and kindness does not create the tension required for a romance novel...
Back to polishing the clock, but some places always do require that bit extra.