Gradually increase your kg/level, reps or control over time. If you did 40 kg × 10 last week, aim for 40 kg × 11–12, or move slightly heavier once you can complete the target reps with good form.
Use controlled movements and a full comfortable range. Focus on feeling the muscle the exercise is meant to train. For glute exercises, your glutes should be doing the work rather than your lower back taking over.
The last 2–3 reps of most working sets should feel hard while your form stays strong. Aim to finish with roughly 1–3 good reps still possible rather than stopping when the set still feels easy.
Simple rule: Get stronger → move well → make the last reps hard.