The first stage is to have a really good look around your garden and decide what you like, dislike or simply don’t understand. Look where gets the sun and when, are you over looked and to what extent; most gardens will be overlooked by some bedroom windows but in practice people spend little time looking out of their bedroom windows – so they are not as much of a problem as a kitchen or sitting room window. While you’re at it consider which plants you like and how much space large plants are occupying, but don’t be too quick to condemn; that large bush could be there to hide a hidden eyesore.
One of the problems with plants is that you are not really aware of them growing; they kind of do it sneakily behind you back, so you just don’t notice how big they are getting. This is where the new home owner’s fresh pair of eyes comes as a big advantage. Have a good dig, metaphorically speaking, in the back of borders; you could be surprised what you find. If nothing else you may well find a lot of underused space. While you’re at it take a good look at the trees in the garden because if these need attention now is the time to do it.
Are the trees appropriate for the garden? Are they going to, or have they got, too big for the garden? If you have large mature trees in the garden do they need a professional to look them over to check they are safe? If the trees need any major work it will both create a lot of upheaval and dramatically change the garden so it’s best to get it done as soon as is practical. Beware there are many very good professional arborculturalist (tree surgeons) but sadly there are also a lot of butchers out there. So check they have a proper formal training, carry appropriate insurance, get more than one written quotation and remember if a price sounds too cheap, and tree work isn’t, be suspicious!
One common problem is people buy Christmas trees with the roots on and then come the New Year can’t bring them to throw away a living tree they’ve spent the holidays keeping alive. Then comes the problem of what to do with it, so it gets planted in a corner of the garden. This all sounds nice and remarkably quite a few of these Christmas leftovers survive, looking quite nice tucked in the border. The problem is the type trees sold as Christmas trees are the type that grow quickly into big trees, which makes sense if you’re trying to produce trees that are sell-able at the best price. You can probably see where this is going, they sit quietly at the back of the border growing! These are not a good choice for a domestic garden. People get attached to trees. So you soon end up with what is in effect a large and growing arboreal pet in the garden. I’m afraid the only realistic solution is to remove it before it gets any more of a problem, or more expensive to remove.