What to include - the background matters!
 

It is easy to get carried away by the pleasant atmosphere of a nice travel destination.
It’s nice and warm, you (hopefully) are travelling with a nice person and the place is marvellous!
You repeatedly press the shutter, only to find lateron that there are many things in your photo that you didn’t realise at the time.

Other people wearing brightly coloured clothes, garbage bins, parked cars...

What a pity! Using a tripod significantly reduces the danger of overlooking such objects in the first place. But even when hand-holding a shot it is worthwhile to check the background.

Even more importantly: decide beforehand what exactly you want to show!
For example, if you want to take a picture of your travel mate in Paris, do you want to produce just a nice portrait? Or do you want to include something typical (e.g. the Eiffel tower or the pyramid at the Louvre in the background?
If so, do you want the background to be as sharp (and important) as the person?
it’s up to you! If you use a wide-angle lens, you can produce a shot that shows foreground and background with equal sharpness, but you may actually distort the face of the person!

Very often, it’s more advisable to use a tele lens from further away. This will show less background and also helps to let the person appear much sharper than the rest of the picture (see “depth of field”).
Also, do you want to show the full body of the subject or just a part of it?
I have seen many shots in which only the feet or the lower part of the legs of a person were missing. This looks very unbalanced - not recommended.
If you want the whole person, leave a bit of space under the feet and over the head.
If you want a portrait or a close-up, just include the part from the waist up, or the face only, or even only parts of the face.

With landscape photos, the background usually will be more in the focus. A wide-angle is often perfect. However, make sure to include something of interest in the foreground when using an extreme wide-angle, otherwise the picture may lack interest.

As for colours: bright colours (especially red)  immediately command interest.
Even small coloured objects in the background may distract from your main subject.

How to take good travel photos