When you are shooting outdoor you always have to deal with the biggest source of light that mother nature gave to us: the Sun. And when you are shooting landscapes, but this is valid for any kind of photography taken outdoor, how to use this source of light is one of your main concerns. For example, if you shoot facing the sun, especially in those rare occasions where even here, in Ireland, the sky is clear, you will get a very bright sky, and it's impossible to have the entire frame exposed correctly, because if you expose for the sky, the rest will be underexposed, if you expose for the land / city / whatever, the sky will be overexposed. Then if you turn by 180 degrees, with the sun on your back, you get a better situation, where the sky is more blue, and the exposure can be a bit more balanced. But then if it's midday, you are screwed. as the sun is on the zenit, and doesn't matter where you point your camera, because everything will look the same: flat.
In fact one of the common mistakes in photography is to believe that in sunny days, when there are no clouds and the sun is high, is the best situation to take photos. That's absolutely wrong. Especially when the sun is high, the light is extremely hard, and the fact that it's perpendicular as well it doesn't help at all. It makes everything look flat, no tridimensionality at all, no depth, just an awfully boring photo.

Same story if you are taking a portrait, despite of what the instructions of disposable cameras told us in the 90s, if the subject face the sun, he will have to close the eyes because he cannot simply look at you, while if you face the sun and not the subject, his face will be in the shadow and he will probably look like a zombie. Hard lights most of the times are just bad for portraits, that's why the best light when you are shooting portraits, is when it's cloudy, where the clouds work exactly like a giant softbox.
But let's go back to landscapes. A few days ago I was scouting for new places to photograph, and I went to Christ Church, a cool place here in Dublin, and I took some shots from the pedestrian crossing right in the middle of the street, with my 6D and the Canon 17-40mm f/4 L, on my trusty tripod, with no filters and nothing else, just to give me the idea of the frame.

It was about 2pm, the sun was behind me, and as I said above, the sky is blue and the picture is quite well balanced, but it's terribly flat, the only shadows you see is the one on the side of the left building, that's it.
Then I tried to add an ND filter, to make it a bit more interesting, especially because I wanted to get rid of static cars in the middle of the street, and I wanted to make the shoot a bit more dynamic.
Things got better, or at least I just got the trails of the cars, the sky is bluer, but still, because of the (lack of) shadows, the image looks flat.
So, how we can "correct" this photo? Simple, by shooting it again in the best hours of the day, the mighty "Golden Hour"! It might sounds like some bollix magical thing from a fantasy book, but it's not, it's a moment of the day when the sun is just behind the horizon or very close to it, when you still get the reverb of the light, with a very intense blue sky, and the lights of the city are turning on, so you get extra light sources, and the ambient light with the artificial light are in perfect balance.
So, after these test shots, which they helped me to find out which was the best angle to shoot (yeah I know, I showed you only one photo, but I've been walking around that place to get all the possible angles, and the one I'm using in this article was the best IMHO), a couple of days after I went back again in the same place, but at a different hour of the day, about 9.30pm, and I took some shots, initially with the ND filter, but then it didn't work well with the light trails of the cars, so I removed the filter and because the ambient light, obviously, wasn't that strong, I could archive 8 seconds of exposure at f/16, ISO 100, and combining four different photos, just for the light trails of the cars, I got this final shot:

With the street lamps and the lights of the buildings, and a more balanced ambient light, I got a much more interesting result, where the different shadows gives me a better sense of depth.
If then you take the same exact shot after one hour, then the reverb of the sun is gone, and the sky is completely dark, and you also lose all the contrast between the buildings and the sky, where only the artificial lights are your only source of light.
I hope this quick, and not very well written article, helped you to understand how not only WHERE and WHAT to photograph, but also the WHEN is a main factor.