I am usually given rough sketches to work from, or previous drawings that are scribbled all over. The main line of CAD drawings I do are electrical so I have a symbol library set up and just connect them up with lines (wires) I have a copy of the Britsh Standard Symbol library for my job and it was just a case of putting them into Autocad
Perhaps you could start with finding out a bit more what the line of work is you'd be doing, be it mechanical, scaled drawings or electrical work hey, you could be designing the next space station then start by looking over the internet for where you can get hold of the standard symbol libraries.
For a excersize to keep you going have you seen the symbol libaries that come with the software? Perhaps with them you could draw up a scaled drawing of you house? I believe they have everything plus, the kitchen sink. If this is not enough try developing your own.
Keep on cadding.