When you've achieved a goal, take the time to enjoy the satisfaction of having done so. Absorb the implications of the goal achievement, and observe the progress that you've made towards other goals.
If the goal was a significant one, reward yourself appropriately. All of this helps you build the self-confidence you deserve.
With the experience of having achieved this goal, review the rest of your goal plans:
If you achieved the goal too easily, make your next goal harder.
If the goal took a dispiriting length of time to achieve, make the next goal a little easier.
If you learned something that would lead you to change other goals, do so.
If you noticed a deficit in your skills despite achieving the goal, decide whether to set goals to fix this.