Starting a Scene
It's important to give careful thought to the point, in the ongoing action, when you want to start writing a scene. A good rule of thumb: Start as late as possible. In other words, when things begin to happen. Often writers do this by jumping right into the middle of some ongoing action.
Suppose a scene involves a teenager getting arrested for shoplifting. Unless you're just introducing the characters, you wouldn't start this scene with the girl leaving home and walking to the store; you'd probably avoid a detailed description of the neighborhood she walks through. You'd probably want to start just before the arrest, when she's looking around and being tempted by what she sees and realizes that she has no money with her, and even if she did, it's all more expensive than what she can afford.
Even though you want to start late, don't forget to orient the reader at the start of each scene by establishing, right away, when and where the action is taking place and who is present.
Here's an example from Olive Kitteridge by Elizabeth Strout. Notice how artfully Strout orients her reader at the start of a scene without making it feel like a dry news bulletin.
At the marina on Sunday morning, Harmon had to work not to stare at the young couple. He had seen them before in town, walking along Main Street: the girl's thin hand — cuffed at the wrist by fake fur on the end of her denim jacket sleeve — had been holding the boy's hand loosely as the two had looked in store windows with the same laconic, unqualified comfortableness they now had leaning against the railing by the stairs.
Strout sets this scene, which takes place in the middle of the novel, quickly and economically. We know when (Sunday), where (at the Marina), and who (Harmon and the young couple). She establishes all this and quickly follows up with dialogue and action as the characters interact.