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Correct size. That might sound obvious, but consider also width and height (of the instep). Each make is a bit different, so there's a need to try on many before you find one that fits really good. For all-day trips get boots one size larger than your usual office shoes are.
If properly maintained, leather upper is much more waterproof and durable than fabric/suede. Unfortunately, it is also heavier.
The fewer seams the better. Boots with many seams, holes etc. usually are not very waterproof :)
Gore-Tex inside is a big plus. Especially for multi day hikes in wet weather, when shoes won't fully dry overnight.
Are you sure you need boots? I absolutely love my trail running shoes (La Sportiva Wildcats). They are much lighter than boots, and while they aren't water proof, they dry out very quickly due to being mostly mesh uppers. On hot days, you can literally feel the breeze through the uppers. It is very nice for me as my feet tend to sweat a lot in boots.