Consider a 30 day challenge. It can be stressful to think about trying to get cleaned up all in one day. Breaking the task into small parts makes this much easier. The internet is full of 30 day calendars and lists to make this manageable. For example, one day you might tackle your Rubbermaid/plastic storage cupboard and the next day you dump out your junk drawer and sort.
Use a 3 box system in the room you plan to declutter. Get three boxes and label them: KEEP, TOSS and STORE. One day you can sort and the next you can execute the plan of putting things away, dropping off stuff to the Goodwill and boxing up items to store.
Enlist help. Sometimes we need an honest opinion. When you are sorting clothes, ask a trusted friend or relative to come over and help you decide what is still trendy and flattering and what should get a new home.
Use the 80/20 Rule. Experts say we only wear 20% of items in our closet 80% of the time. This principle works with kitchen gadgets, children’s toys, boardgames, etc. Figure out your 20% (with some wiggle room!) and donate the rest!
Be ruthless in your first sort. Then sleep on it. The next day if you still are OK with getting rid of an item, then you are making the right decision. Giving yourself an extra day to decide if you love the item makes it not so difficult to decide in the moment.