5 steps to help with decluttering:
1 - Start with your trash. Throw it out.
2 - Do your easy things next. don't put things in a pile because this will keep the clutter around. If you see something that has a home, put it away.
3 - Keep a box handy that can be used for donated items. Only add things that are worthy to be donated.
4 - First ask yourself, "If I need this item, where would I look for it?" If you can immediately think of a place for it, put it there. If you can't, ask this question, "If I needed this, would it occur to me that I already have one?" If you don't use it often, donate the item.
5 - Make it fit. You can only keep items you have space for in the place you are decluttering.
Work through these steps in small places and you'll make progress without getting overwhelmed.