Just keep a good, safe distance, especially from bird nests and mammals. From my experience, mammals, once spooked, they don’t usually come back again. So, if you have a choice, take photos from away, but you can hope that animal might return, and, perhaps, get used to your presence.
Apart from the clothes, never forget your camera or phone - you never know what you might find. I got used to carrying my camera in many places I go to, just in case I find some cool organism.
As for clothes, get informed about the location where you’re going observing, the weather there and what habitat you’re going to (wetland, desert, grassland or something else), so you can take the proper clothes with you.
In most of the times, it depends where you want to go. Forests, mountain trails and wild reserves are best visited in groups, as you never know what you might find (in Romania we have a SERIOUS problem with brown bears).
Sometimes though, you don’t even have to go far to see cool organisms. For a start, you can just visit your backyard - it’s amazing to see what you can find in a garden if you wait long enough, sometimes it’s a matter of minutes until you find a new butterfly, bird, insect or, who knows? something else.
Communities are a great way to interact with people with the same passion as yours: for example, I joined the eBird community this year, as I’m specialized in ID-ing birds (even though I mostly observe bugs 
). As you find your own favorite things to observe, you’ll find the communities you’re interested in easier.
As for me, I consider iNat a community big enough for me to stop searching for something else 
). Thank you!