What metering mode is your camera using as you take these shots?
For example, the challenge in a landscape can be the amount of dynamic range you have in just one scene. White puffy clouds or snow capped mountains will meter at one setting (which will be very bright) and deep forest details will meter at something completely different (which will be very dark.) If the camera is metering on what it just happens to be pointing at then you can lose one or the other (highlights or shadows might end up clipped.)
You can slow down -- look (with your eyes... ignore the camera for a moment) to find the brightest thing you can find and then also the darkest thing you can find and try to meter those two things on their own. Some hand-held meters are better at this than cameras -- spot metering with a camera is usually 3º or maybe 5º, but a spot meter with a light meter (usually only high end light meters can do spot metering) are more precise and meter within a 1º angle. Regardless of the equipment, it's the CONCEPT that you want to learn. By ignoring the cameras generalized recommendation for scene-wide metering and you looking for the specific highlight and shadow points and then find the middle exposure. Your camera can almost certain handle several stops of dynamic range up and down from the selected exposure. As a result, you probably won't get blown out or clipped shots.
If the sun is in the scene, don't panic... but also don't try to compensate for the sun. It'll be blown out... no matter what you do. Unless it's very close to setting and has managed to get toned down to an orange ball, it's going to be blown out.
For portraits where you struggle with lighting, it may be that you're not using a flash. Outdoor sun on a subject creates a HUGE difference from the illuminated half of a face and the shadow half of a face. Using a flash (even if it's just your pop-up flash... it's one of the very few things that a pop-up flash is good for) can help fill in those shadows.
Stops of light are exponential. Each stop brighter requires a "doubling" of the amount of light present. Yet your flash is putting out a fixed amount of light. That means that, as a percentage of flash contribution, your flash will contribute GREATLY to brightening the shadows but it will NOT contribute greatly to making the highlights even brighter. That works in your favor. It allows to even out the light in a scene. The goal isn't to make the shadows as bright as the highlights (that would just result in a really flat looking photo). The goal is just to decrease the number of stops of difference between highlight and shadow. By filling in the shadows so that they're just a little dimmer -- but still retaining shadows to show some 3D dimension in your photos -- you get a better result.
When I look at a scene I think "What can I control here?" I know I can't control the brightness of the sun -- unless I learn the secret to conjuring clouds out of nowhere. But I might actually be able to control the amount of light in the shadows. Sometimes the solution is to just shoot the subject somewhere else. If it's a portrait, then presumably you can control where you ask your subject to stand. For landscapes, sometimes it's a matter of shooting when the light is favorable to you. This might involve you getting up extra early or making it a point to be there at the right time. I know the world is full of great photographers who make all these shots look like common photos they can just take anytime they want... but quite a number of those shots weren't really taken "anytime the photographer wants" -- the photographer had to make some accommodations to their schedule to get those shots.
Understanding Exposure is a great book (and watch his videos too). You might want a book on lighting. Sekonic (manufacturer of handheld light meters) has a video series that's VERY educational.
You might want to watch these:
Control the Light and Improve Your Photography: Part I — Portraiture Using Available Light
Control the Light and Improve Your Photography: Part 2 — Better Environmental Portraiture
Control the Light and Improve Your Photography: Part 3 — Studio Portrait Lighting
Control the Light and Improve Your Photography: Part 4 — Creating Great Landscape Photographs
They probably run about an hour each, but Joe Brady does a great job breaking it all down in a way that makes sense of something that would otherwise seem like a black art.