It's not something you have to be terribly worried about while you're shooting, though it may be a good idea to carry around a white sheet of paper. Shoot a few test shots with the paper in frame and use those shots to properly set your white balance on your final photo.
As for exposure, here's a couple of tips that helped me out when I first started out:
First and foremost, aperture is for depth of field. Yes, closing the lens allows less light to pass through to the sensor, but it changes the aesthetic qualities of your photo. I would not advise getting in the habit of changing your f-stop to lower your exposure. There are other, better ways to do this.
Second, if you're using an SLR, invest in neutral density (ND) filters. These are basically sunglasses for your lens. They will lower the amount of light going to your lens by the specified number of f-stops, allowing you to take pictures in daylight without blowing out your image.
Third, it is easier to correct exposure if the image is underexposed than it is if the image is overexposed. The reason being your sensor takes in a whole lot of information, and your imaging software "decides" what information to show you. In underexposed images, it is showing you less than is actually there, and by cranking up your exposure slider you can reveal otherwise hidden detail (to a point). But you can't as easily crank the slider down to reveal detail you accidentally overexposed. For this reason, I typically shoot for a -1 EV rather than a dead-on correct exposure.
Fourth, time of day is critical. The hour after sunrise and the hour before sunset are often considered the best times to shoot outdoors, as there is less light, and what light you have is made more dynamic (colors & shadow). Personally, I think you can get good shots in the early morning and late afternoon, but it really depends on your subject (see my last point). Whatever the case may be, avoid shooting in the middle of day. There's too much light and too little shadow.
Last, expose your subject and not the background. This probably won't apply if you're shooting landscapes, but it could be invaluable if you're shooting portraits or wildlife. As long as your subject is properly exposed, your background can be dark or blown out. When there is significant contrast between my subject and the background, I turn on spot metering and expose for the subject rather than the whole scene.
To adjust color mode in Lightroom, go into the Develop tab and scroll all the way down to "Camera Calibration". The color profile is set to "Adobe Standard" by default, but you can select one of your camera's profiles from the dropdown menu.
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