Hazards

Generally speaking this is not an especially hazardous undertaking, within the overall context of trekking in Nepal. I have mentioned Altitude Sickness (as a non-issue) elsewhere. Here are a few other things to be aware of.

Transport
Without doubt the highest level risk is the transport to and from the trek. Buses as well as planes are significantly more risky in a country with poor infrastructure, institutions and standards than they are in Europe or the US.

There is no useful advice that will keep you safe. Having a bit of food, water, and a book to read will keep you slightly less uncomfortable during the inevitable long unscheduled stops. Oh, and take advantage of every possible toilet break.

Off the trail
Once on the trail, there's much less that can go wrong except falling off it. At times the trail can be a little narrow so it's worth paying enough attention so that you don't plunge into a yawning abyss. Assuming you don't, then it's mainly a matter of looking after your health. 

Water
Step one is to take care of the water you drink (and drink lots of it). I have mentioned the magic SteriPen under Gear, but whatever water purification system you employ make sure to use it all the time. Or drink tea (chia in Nepali). 

The next rule is the usual one Don't put your fingers in your mouth.

First Aid and Pharmacy
Do carry an adequate First Aid Kit and Pharmacy. Most medicines and materials are readily available in Pokhara but specialty stuff for specific conditions will be obviously something you'd bring with you from home. There is nothing worth mentioning in the way of medical facilities in this region. 

Then there is the additional problem of what to carry in case a local needs some help, and what it is ethically reasonable to do and to provide. There is quite a good discussion of this in the Lonely Planet "Trekking in the Nepal Himalaya". The section on medical matters is disquieting but quite comprehensive.

Animals
We didn't see any dogs that were especially worrying but it is certainly worth paying attention to them. You'd probably be considered lucky rather than unlucky to encounter a leopard, and a snow leopard would be beyond fortunate. More likely you need to pay attention to a pushy mule going past and stay on the mountain side of the trail. We met no yaks as it is too low altitude for them.

Other people
Drunks are annoying but not much of a threat. There will doubtless be some bad guys somewhere, so travelling as two and not walking at night seem fairly sensible precautions. But compared to walking around many cities in the West it is pretty low risk stuff. It would be wise to hide out of sight if you do decide to camp. 

For women
Women travellers will be already exercising their usual precautions. Just bear in mind that the status of women in Nepal is towards the opposite end of the spectrum from (say) Iceland or Norway, but a bit above (say) Somalia perhaps. You will inevitably be the centre of attention, whether this is welcome or otherwise. There are plenty of women travellers who have written on this subject with more authority than I can. I'd be good for all of us to read them and learn.

Low door frames
Now we are talking about a real day to day risk. This is something that I never seem to remember in time. Short of wearing a cycling helmet you just need to duck a lot. Paradoxically this is probably much easier for people who are very tall, than for those of us who keep forgetting that we are considered tall in this country but not elsewhere. 

A friend of mine found himself getting 11 stitches across his forehead on his first day in Pokhara. Nasty!