This is like warning bells that someone is about to buy new boots and then go on their first hike.

Three simple hiking rules:

1) Never wear new boots on a trail. Sittin in the office, sure. Walking around the grocery store, sure. Walk around the block at home, sure. A day of yard work, sure. But never wear new boots on a trail. Many groups will kick you out and send you home if your boots aren't looking old and scruffy enough, nothing personal they just don't want to have to do wilderness rescue on you.

2) Bring more water than you think you'll need. Newbies always guess low. If you're feeling thirsty you've already failed. If you don't end the hike with water leftover you've failed.

3) It's considered very poor form to have to ask someone else for first aid stuff, although its considered even worse form not to help someone who needs it, and the cheapest lightest smallest kit is probably about right. Doesn't have to be some giant backpack a little pocket sized thing is fine.

Everything else you can learn from the group. Leave No Trace philosophy and orienteering and all that stuff. Which is an excellent conversation starter, where did you learn to read topo maps, what kind of plant is that, etc.

Depends very much on the group. Some are super hard core and love nothing more than hiking 30-40 miles at a quick pace over mountainous terrains before building a bivouac and eating a freeze dried meal, while others are super relaxed and love nothing more than taking a leisurely 7 mile walk and ending up at a nice pub. Ask around and try to find a group that fits you.

I'd been biking around 10 miles daily prior to it, but was still hit hard by my first hike. It was about 8 miles with a 2,000 foot climb, and I could barely walk for three days after. A few more hikes, however, and I was reasonably well conditioned. Well worth it, but could even be avoided somewhat with a more reasonable few starting hikes.

it's hiking, not lsd :)