The viewpoint you take up will affect the angles of the things seen. It will affect your foreground and, by being either up or down, change the middle and background too. If you are high up you will see more background; you will be looking right down on to things.
If you are set low you will be looking up at them. All this may sound obvious, but it is amazing, when we first start drawing outdoors, how easy it is to forget the obvious.
In selecting your viewpoint don't be timid about letting any object, a tree or a lamp-post, sit right in front of your vision. An object, close to you, that you have to see round or through, makes an excellent foreground, and will create an interesting lead into the middle distance.
Similarly, a line of the road that shoots away and enters into the center of the picture, will give movement. Avoid the viewpoint in which all the angles are either horizontal or perpendicular. This tends to create monotony. Look for angles that move down or up. Movements that are inherent in nature, but which are so difficult to pin down into a small rectangle.
Color should be used sparingly on the first few outings, and at best should not be used too lavishly. If you start flinging color all over everything, you will destroy the very point of using color. Color can be very effective for giving just that extra kick to a black and white drawing, as long as it does not swamp the drawing altogether. Restraint when painting is necessary. Your control over what you are doing is lessened if you use too many colors. Mix, at first, only the very obvious colors you can see, avoid attempting all the subtle halftones. Better to draw those in, than to try and work out how to do them. If you have one or two important colors to deal with you will find that they will be sufficient to give liveliness and sparkle to your sketch.
This applies to both opaque and transparent watercolor, though it is probably easier to get the halftones more successfully with transparent washes, it is still better to use restraint.
Drawing people outdoors is a little difficult for the one good reason they never keep still for one minute, and as soon as they spy you doing a sketch of them either take umbrage or hare off immediately. It is possible to go into a crowded place with a small sketch book and discreetly draw people as they move about. But this is not easy. It needs an iron nerve and a good eye.