When looking for a new skatespot, the first key is to Keep Your Eyes Open. There are places to skate all around us, especially if you live in a city! Take another look at all of the places around you. Watch the places you pass on your way to school or church or work. Look behind buildings, take a walk or drive around, looking at things with the question in mind, "Can I skate that?" There are all kinds of hidden places just around the corner in cities.
Even a simple flat secluded parking lot can be a great skate spot, if you bring in some obstacles! And that's the second key - Be Creative. You don't need a funbox to ollie over - try ollying over pop cans! Or your buddy's skateboard! Don't have a portable rail? No problem - look for ledges, curbs, benches, anything. C.R. Stecyk III once wrote, "Two hundred years of American technology has unwittingly created a massive cement playground of unlimited potential. But it was the minds of 11 year olds that could see that potential." Get creative!
If you see a spot that you think might work, but it's on school, church or work property, Feel Free to Ask. You never know what they'll say - and they might respect you more for asking. The pastors at my brother's church let skaters skate their stairs and rails, but only if they ask. If you are afraid to skate the spot, they you have nothing to loose by asking!
If you live in a small town, then it might be a little tougher to find good skate spots. You might need to use some last resort spots, like your driveway or garage. Rodney Mullen started skateboarding in an area like this, and now he's the best skater in the world (in my humble opinion!).
The third key is to pay attention to No Skateboarding Signs. If they are there, then don't skate the place! I know it might be tempting. That's why there's a sign there. But if you DO skate a place like this and get busted, then remember that you knew they didn't want you there, and it's your fault, so play it cool and don't get mad.
Once you do find a spot, invite some friends and enjoy it! But remember the last key - Don't Trash It!. If you have a good spot, don't be lame and graffiti the place up, don't leave garbage around, and don't break stuff. That will ruin the place, and likely get you kicked out and a "No Skateboarding" sign put up. Don't be the guy who ruins it for everyone else.