uh...maybe this isn't so easy

So my hedges in front of my house are starting to loose their shape, so I decided to trim them.

I got these hedge trimming clippers (non-powered) when I got my lawn mower. so I started cutting...How does one keep it in a straight or curved line to get the shape desired? I don't know...they are trimmed...I guess...but they probably need to be touched up and evened out.