It's really not that hard, you just have to know what you and your family like, everyone's daily activities and routines have to be considered when you are making big changes.
An example would be, say you put a shrub or flower garden right in the center of the backyard, is this going to keep your children from being able to play different kinds of games?
You'll want to have your children playing at home and have their friends play with them too, so it's very important not to affect the area they need to play in.
Don't put things where others like to walk. Maybe it's a route to a mailbox or the path the kids like to take to their play area.
Either way, don't plant something that will change how people are used to traveling around the yard, you may find that they get very upset.
Maybe you want to add something to your backyard landscape that the whole family would enjoy.
Maybe a bigger deck, a hot tub, a bigger swing-set, etc. Just be sure that your budget can handle what ever it is that your family decides to get.
Be sure to think about any future additions to your family when your making plans. If your children have grown and gone you may still consider putting in a swing set or sandbox to your design for the grand-kids that soon will be coming. This way they'll have an area to play in when they are visiting you.
As you consider what you may like to put into your design project, it would be a great idea to begin keeping everything in a folder so you can place all your ideas and pictures in one place.
You may want to write all your landscape design ideas down in a notebook as they come to you, like when you see something you would love to do in your own backyard landscape.
When you are ready to do the final draft of your landscape plans, you can pull everything out and you're ready to go.