My tips would be to start with the following.
Wherabouts in the country are you? and are you inland, on the coast, surrounded by woodland, open aspect? is it windy or particularly shaded? Any information you can give to describe your plot will make a difference to recommended plants.
What aspect does your garden have? what size is it and what defining features must be kept - any fences, trees etc.
Most important, what kind of soil do you have? Clay is heavy to work, waterlogged in bad weather and rock like after direct sun, but it will hold nutrients and roses love it. Fine and sandy sand is the opposite of course.
I've started a few gardens from scratch and started with how much work I wanted to do longer term. I sketched out schemes bearing in mind height and spread of chosen plants and I shopped at local markets, WI sales and nurseries where the plants had been grown rather than garden centres - this is cheaper and it's likely the plants will thrive.
Don't forget to consider your preferred colour schemes and also the kind of planting scheme you take pleasure in. It could be hot colours with quite an architectural appearance, or it could be softer colours with a soft drifting scheme. Best thing is to work out some focal points and then spread out from there. Think about statement trees, shrubs or plants, if you want a wildlife area, a water feature, a potting shed and so on and go from there.
Take a look at some famous gardens where you can see images on line and see what most takes your fancy for inspiration.
Sissinghurst gardens can give you ideas and inspiration, the website also has a blog to follow or go to www.gardenersworld.com and www.rhs.org.uk/advice/design