Here is probably one of the most important tips as far as safety. Don't hide your spare key near your front door. Places like under the welcome mat, inside a fake garden rock, or in your mailbox are not the best places. Thieves are smarter these days. Those places will be the first place they will check.
For a more secure place, leave your spare with a neighbor your trust. If you don't like that option hide it somewhere else around your house or property(i.e. garden shed, potted plant, etc.). These places are not easy for a thief to find.
Hope it helps!