1. You can get some art work put up. get an accent wall/ceiling

2. Change the wardrobe shutters if in budget.

3. Change furnishing like curtains and bed linen to something that goes together with the fresh vibe

4. Add some pop of colour with highlights

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Darker curtains are blocking out light. Consider lighter color. Also choose light weight flowy fabrics. You can combine heavier curtains with light ones intertwined. So you can use them according to your requirements. Since you have a lovely window with your own terrace I suggest you to leverage that. 

Consider washing the paint if it's washable or just refreshing the paint with a light coat.

Move the bed closer to the window, removing the piece of furniture in between. You can get two side tables made out of it or consider getting new ones to bring a sense if balance. These tables can house your books and the stuff in the small open space above the computer. In this open shelf now, you can keep small decorative pieces according to your decor. Also add a simple lamp for a lift.

You can go with overall lighter color scheme with giving a pop of color with different darker color bedsheets.

Consider changing the sunmica of the wardrobe. You can match the color with the glass door. Or go completely light, which would really open up the room. Suggesting to go with plain instead of any embossing or cut out like designs on it.

Consider Increasing some storage according to your needs as this would also get room more orderly, allowing you to focus on your decor.