A trend in many older roleplaying games that has been reversed is seeing humans as the default species: no special powers or abilities of course. After all other people don't look like anything special do they? The accuracy of that portrayal is up to debate until we meet other intelligent lives or discover elves and dwarves exist.
Recently games such as (A)D&D have tried to address this by letting humans start out with extra skills or feats (not feet) to balance the natural abilities of elves and dwarves (detecting secret doors is obviously evolutionary gold in a world of dungeons, monsters and tombs.) Otherwise who'd take a human? Previously they merely capped the experience level these long lived, intelligent, and resourceful beings could attain.
A lot of people have remarked on our warlike tendencies and assume that when we do reach the stars our combination of warrior heritage and engineering Masters will make us a potent force. I don't buy it. There are no soft targets among those who play evolution's game. Even if you assume a race has evolved beyond the need for chronic confrontations and violence they'd have had to develop ways to deal with those who did not evolve in their own populations and with external threats.
Looking at humans and our place in nature we have one physical attribute that makes us scary: we don't give up. When we hunt prey we will follow it until one of us dies. We pursue relentlessly. In the past primitive humans harried gigantic beasts to death using only spears and their feet. We display this persistence in many of our endeavors.
Earth has an oxygen atmosphere. The proportion of oxygen might be an important issue in colonizing other planets. We are used to an atmosphere containing 21% O2. We can survive in an atmosphere of 17.5% and probably extend this with meds, compressor masks and what have you. What I was thinking was that oxygen is a very corrosive element that, even though vital savages our bodies over our entire lives. Look at Michael Jackson's odd sleeping arrangements for more on this. What if aliens are just not able to take in atmospheres with such a high concentration of oxygen without severe and short term health issues? We might have a wide swath of Earth-like worlds left behind for us to grab. If oxygen breathers are a minority we really score!
Being able to absorb all this oxygen would also mean we are relatively fast and energetic compared to life evolved in low O2 atmospheres.
While I'm on the subject of breathing humans can hold their breath longer than any other terrestrial mammal. Make of that what you will. It might mean we have a longer period of useful consciousness after our ship or spacesuit gets holed than other beings.
Another edge we might have is in microbiology. H. G. Wells was the first to bring up the subject of native microbes being lethal to offworlders who have no resistance. Many believe that the ecologies of alien worlds might be incompatible. We can't eat them, they can't infect or eat us. Assuming a middle ground: we can eat some stuff etc. our microbiology is pretty ancient. Moore's Law (see http://twilightgm.blogspot.com/2014/06/hiding-in-plain-sight.html) predicts life evolved 10 billion years ago meaning either we underwent a spate of sudden evolution spikes or our slimy ancestors came from somewhere else. Either way the microbes here might be a very dangerous lot and we concurrently evolved to deal with them. So in game terms we would have fantastic immune systems and might be able to eat darn near anything compared to most life. Note that if life did come from somewhere else then exoplanets might have similar biologies to Earth's assuming the microbes or whatever from the original planet were dispersed to more than one world.
Finally please check out this PSA from the Galactic Safety Council: