If you were to go and stand in the center of your yard and look at your planting beds what would you see? You might see some plants thriving and looking very well and you might find others that are partially sick and you even might find some that grew too quick for their spot.
The key to good looking landscaping is to understand balance and flow, simply put, taller in the back, medium in the middle and lower in the front. The other thing you need to know is that shrub placement should be in the form of groupings rather than one of this and one of that.
Large showy specimen plants should be strategically placed between windows and on corners so that they can stay in that spot for many years into the future. You may want to study some beautiful landscapes that appeal to you and this way you will be able to figure out what it is about it that you love too much.
I can tell you now, that there will be a rhythm to the landscape that you admire and this is only because time and thought has been put into it.