Ok, so there isn't much planting in the garden at the moment, so you aren't likely to ruin anything.
Lots of planning is a good idea!
So
mow the grass and keep it mown this summer, that will allow you to use the space and think about what you want.
Think about garden use and your family - do you want to eat outside? BBQ? play area for kids? football patch, or just a sandpit?
Think about the amount of time you have, just enough to keep it tidy, or take it up as a hobby (eg one day per week)
Think about you budget, a decent bush is £20, and small, and then in 5 years will fill the space.
Look at where the sun is, not just now but over the summer, and whether that is a good thign or a bad thing, eg in spring I love to have coffee in the sun, in summer I love to have coffee in the shade!
Do you want to do things like grow veg? (if you do that seriously it is a lot of work, but you can stick some runner beans and tomatoes in anywhere and it is fun)
Look at what is not going to move, eg large trees, fences, sheds, paths. Do any of these need some work eg trees need cutting back as giving too much shade/too old
Also think about being inside. I have planted things that I can see form our french windows and kitchen window in the spring, when it is raining and I am stuck inside.
What parts of the garden can you use to your advantage, eg the garden wall can trap the sun and make a great warm backdrop for something like a vine, clematis, climbing rose, even a peach tree!
OK, then plan where you would like bushes and colour.
2 types of perennials (ok I confess I might not be using correct terminology here) one is basically a bush/tree/plant that has interest at different times, eg flowers in the spring and fruit in the autum. Some of these look pretty over winter (nice shape, coloured branches, stay green) others are bare and boring all winter, which is fine unless it is the ony thing you see out of your kitchen window.
The other are things that come up every year, but disappear completely in the winter. There are some lovely plants that do this (eg daffodils) but they do leave a hole in the winter.
Then there are things that you plant once for this year. You can usually buy strips of cheap bedding plants, bright, colourful and will grow into a big pile of flowers and last until the first frost. They are really useful for adding colour to a garden. especially if you are new.
If you can't wait to get stuck in, then chose a patch you can see, and plant a few strips of bedding plants, enjoy them and the colour while you start to plan and sort the rest. Or plant up a few tubs pots with them and stick them round where you like to sit.