The ultimate goal when locking up your is to not have it taken. My father tells me stories of how he and his friends would ride their bikes to school and just place them in the school style rack (grill).
While this may have worked for my father in Wisconsin, in the 1950s, it will not work today.
However, no matter what you do, there will always be a way to steal a bike. You may have the best locks in the world, but if the rack or pole is weak, then you have a weakness.
All you can really do is make it hard to take your bike--discourage the theft. In a sad way, your goal is to make the thief move on to another bike.
Place your bike in a visible area. Do not leave your bike, on a rack, outside, overnight.
I have a hub generator so I throw a cable around the wheel and attach it to my U-Lock (locked to frame and rack).
This type of cable is not hard to cut through, but I am creating a deterrent. I will replace this cable with a more durable one when I can.
In some ways, the presence of several locks will send the message that "this bike" is not worth your time. (You could argue that several locks says "steal me because I must be worth a lot of money," but I have not found that to be true.)
I have a rear wheel lock. This type of lock is great for use with other locks, and especially that time when you get to the library and realize that you do not have your U-Lock with you. It works for a quick jaunt in and out. Or when you can see your bike from your cafe chair.
I recommend purchasing a rear wheel lock because you will always have some lock on you. Remember ... deterrent.
I have another cable that goes through my seat and back to my U-Lock. You can take out the quick release on the seat post and put in an odd-head-bolt to achieve the same purpose.
Then the U-Lock which connects my frame (the bike) to the rack.
This may seem excessive. However, it does not take long to set up and I figure less than a minute of time is worth having my whole bike there when I get back.
Locking up your bike (well and securely) is a good habit to get into.
I have posted this video before, but it warrants posting again: Hal Grades Your Bike Locking.
Photos taken with the only camera on my person that day--my phone. Funny how we have accepted lower quality photos for higher convenience.