1. Start small.
A drawer, the towels, something unemotional. Complete that task fully to set yourself off to a winning start. Before and After pics can help you stay motivated and prove how much progress you've made.
2. Schedule breaks.
You'll want to power through if you're on a roll but decluttering and making lots of decisions is more tiring than you realise (decision fatigue is a recognised thing!). Set an alarm on your phone for once an hour/90 mins. Plan the area you'll tackle after the break to avoid feeling paralysed when you return. Step outside the room. Have a glass of water. Have a cry if needed! You'll get way more done this way I promise.
3. Leave Sentimental Items 'til Last
Leave anything sentimental or emotional to the end so you can deal with that stuff all in one go. Getting sidetracked by old letters and photos in the middle of an upturned room can derail the whole process. These items can bring up emotions unexpectedly so plan to deal with them calmly and slowly. Mind yourself while you're doing it.
4. Find New Storage at the End
Don't start finding new storage for items until you've fully culled what needs to be culled (and don't buy new storage until you've fully decluttered - you won't know what you need until you've cleared space). Setting up a room again after a clearout is a lovely thing to do and really helps you appreciate your possessions but it's important to complete the clearout first otherwise things will get messy!
5. Rehome Items
If you're planning to rehome items (and that's obviously way way better than just dumping them) I would schedule a time in your diary to do the drop off to the charity shop, the women's shelter, animal shelter, etc (I have a highlight on my Instagram page @stuffhappensemma about where to send things). Otherwise those bags of unwanted items might end up finding a cosy home in your hall/spare room/car boot and you'll be tempted to go back through them.
Above all go easy on yourself and remember that this process can be difficult for all sorts of reasons. If you're really struggling with making decisions try and focus on one small area (like one cupboard) rather than staring helplessly at a whole room. You'll get there if you take your time and stay kind to yourself throughout.
For lots more great advice, check out Emma's book "Stuff Happens! Manage your clutter, clear your head & discover what's really important"