As a starting point, decide to do one box or bag a day for a week or so. (Remember, it's a starting point.) One box is not so overwhelming. It takes maybe 10 minutes, but can make a big difference.
- Go around and fill a box with things you don't love, need, or use but could be donated to goodwill. Once filled, put it directly in your trunk. Do NOT look inside it again. Drop it off next time you are out and about.