We are almost into winter. I'd save my strength and let the cold weather and wind do the work for you.
What sort of winter flowers do you want to plant?
I'm no expert! But first check your aspect - watch the sun through the day, to try and get an idea of different areas of the garden. What is hot and what is not. What is shaded, sheltered etc. That will determine some of your planting, seating and structure. Look out your windows in the house where would you want to put your prize specimens? You might or might not want to shade windows with future growth.
If you do have trees in mind, I'd recommend getting them in early, you normally plant them during the dormant season (I think that's Winter: November to March in the UK.) You'll then have some structure to plant around. Having said that you don't want a tree in the wrong place, so don't rush in if you are unsure. You can always hire an opinion. Or get someone to plan the garden.
There are many books for inspiration, as well as other gardens. Our garden looks very different in the Winter to the summer, as the leaves fall, and for me I like some winter interest. You may want some evergreens for privacy etc.
Soil types, and wetness can also determine planting. I have a chalk garden so some plants and trees are a no-no. Glance your local area, chances are that if it works there it will work for you.
In your situation I'd take my time getting to know the garden and finding out what you want from it as Wayside has said.
In the meantime I'd buy some biggish pots, some multi-purpose compost and some spring flowering bulbs - tulips, narcissus, daffodils, crocus and hyacinths.
Some ideas here
they'll look gorgeous in the spring and give you something to enjoy while you work on the bigger plan
I'd rake it into a pile and leave it over winter. For a start it'll provide small mammals (hedgehogs, woodmice etc) with somewhere to over-winter
Then in the spring, when the hedgehogs have woken up and you've decided where the permanent compost heap is going to be, it can form the basis for that.
If there are any seedheads on the rubbish I'd try to remove as many as you can and bin them - you don't want your compost full of seeds!
If you want to take some photos and post them on here we can try to identify things you may not be sure about, spot treasures and give you some ideas of your options and the best plan of attack.
To post photos on here you need to click on the green tree icon on the toolbar above where you type your post, and follow the instructions. Afraid it doesn't work for iphones, yet ...
If you need any help just yell