Toss deeper into the court, raise the contact point as high as you can, and hit UP on the ball.
Flat serve is a misnomer. Unless you're a gaint you need some spin to keep a "flat" serve in the court. Too often flat serves are hit...flat. And those go long or into the net since the window for a fast ball serve is so tiny with less spin.
Graphene Prestige S mod: 337g, 8.5 HL, SW 328
VS Touch Black/Focus Hex 1.23 @ 58/54