Something you could experiment with: Clear yourself and the room before going to sleep. Erin has a good write-up on clearing your chakras
here. Then clear your room. Say or think loudly something like this: "Only beings of love and brilliance who work for my highest good are allowed here." Ask the beings of love and brilliance to surround you and fill your room, and imagine them repelling darker entities.
If you want to be even more thorough, include your whole house. Mentally explore each room, looking for dark spots. If you find a dark spot or something that feels negative, address it specifically and insist it leave, repeating the phrase. If you encounter a stubborn entity who refuses to leave, ask a being of love and brilliance to escort it away.