First make sure that you have a clear vision of Lara, of what she is to you and how you'd like her to be. Then give her an interesting counterpart, not any lame baddy but someone who can stand his ground against someone like Lara. And/Or put her in an interesting setting; a unique location.
When you have an idea, start writing. (A little music might inspire you, something that gets you in the mood of what you want to write.) Don't stop because you are unhappy with a particular scene but you've got ideas for what happens next. Work through it and put anything in as a placeholder. At the "end of the day" put the story away and pick it up again a few days later. Now you might want to make changes and eventually you will be able to fill a gap. You might even drop whole scenes, but that won't matter, you've lost nothing but you gained experience.