I bike commute and just moved to a tiny third floor walk up. I was willing to give up some of my precious space to store the bike, but it turns out that the narrowness and curvature of the stairs makes it extremely difficult to get the bike up and down. If I was going to store the bike outside, what is the safest way to do so in terms of lock configurations? There's a thick lamp post that I can see from my apartment that I'm considering locking it to. Thanks!
To get a bike through narrow or awkward spaces, hold the handlebars and pull it up onto its rear wheel so it is pointing straight up. It relatively easy to balance a bike like this and push it around. In this orientation it's about as wide as a person and can be turned in place. It's easy to go down stairs and it's even possible to go up stairs by walking backwards with it. The rear brake can be used to stop it slipping backwards.
If you use this technique you may find you are able to more easily get the bike into your apartment.
This depends a lot on the city; different cities allow you to lock up to different things, and have different crime rates.
For example, I've been to major European cities where a lot of the bikes were happily locked where they would have been stolen in minutes in New York City.
I'd first start by removing things that could be easily stolen (lights, seatpost, etc.) or fastening them permanently / locked to the bike (e.g. using pitlocks on the seatpost). You can also glue in ball bearings into hex heads. Pitlocks can also be used on the wheels as an aide to locking them properly.
Then, use a good U-lock properly (leave minimum amount of space for someone to jam a jack in, difficult to cut) and a good quality chain if you're at home (so you have 2 tools). Make sure to grab the wheels (rim is sufficient) and the frame.
Also, make sure to lock to something that is safe to lock to (people have cut down small trees to steal bikes, or lifted something chained to a post over a post; or some things aren't as safe as they seem to some people, e.g. street signs which are often easily removable). The light post may not be a good idea; depending on the city, the police may cut the locks and impound the bike.
In spite of all this, there is a decent chance that a bike will get stolen in a tougher city; having a cheaper bike outside as a beater and taking out a nicer bike periodically (stored in your apartment) can help.
Alternatively, you can carry your bike into your apartment. It's inconvenient but its probably the safest option you have. Note that none of the above options prevent vandalism of the bike (as pointed out by Michael in the comments), which may or may not be of concern in your city.
I successfully keep a cheap old bike in a theft-prone area.
I'm on my second in 4 years because the first deteriorated, not because it was stolen. I use a good D-lock (it cost about as much as the bike, that is £/$/€30-50) through both chainstays to a bike rack. This secures the back wheel as well as the frame. The front wheel has a cheap cable lock through it, and the frame, to the rack. Both wheels use old-fashioned nuts rather than quick-release skewers.
我是4年來的第二個，因為第一次惡化，不是因為它被盜了。我使用一個很好的D型鎖（它的成本與自行車一樣多，即£/ $ /€30-50）通過兩個連鎖店到自行車架。這樣可以固定后輪和框架。前輪有一個便宜的電纜鎖穿過它，框架和機架。兩個輪子都使用老式堅果而不是快速釋放串。
I haven't had problems with the saddle being taken; again it's a nut rather than a QR. Accessories (pannier rack, bottle cage, lights) are attached using anti-tamper torx screws, though this didn't stop half my front light being stolen. The back light has been damaged (vandalism?) more than once, but is securely fastened to the pannier rack. I try to run with everything fixed to the bike as whatever I take off I have to carry on a longer ride (my commute is bike-train-bike with this only used for the 2nd ride).
我沒有遇到馬鞍問題;再次，這是一個堅果而不是QR。配件（車架，瓶架，燈）使用防篡改torx螺絲固定，但這並沒有阻止我的前燈被盜一半。背光燈已被損壞（故意破壞？）不止一次，但是牢固地固定在車架上。我嘗試用固定在自行車上的所有東西來運行，因為無論我起飛什么，我都要進行更長的騎行（我的通勤是自行車 - 火車 - 自行車，這只用於第二次騎行）。
The bike is also security-marked and has a big sticker saying so. The local police do this for free every few months otherwise it's quite pricey. One of the biggest deterrents though is that it's locked up near more expensive bikes (at the station), but at least as well as them.
I would second mattnz suggestion. Try a 20" folder, I have commuted on one for several years, and it was fine.
They are quite small folded or open. Easy to get up stairs and much easier to hang up in your appt compared to full sized bikes.
Many other advantages for the urbanite: easily goes on buses, cabs, metro, and easy to scab a ride with friends part-way on any journey.
The disadvantages are just the imaginary stuff that moaning myrtles always come up with.