Could some of you list these things. Things they should realize before doing so or knowing when to.

For example I just hate it when a jungler decides to jump in on my opponent without previous verification, ping, statement etc. Or when they don't realize the amount of health or mana I'm lacking at the moment.

I agree. It's hard to know when a jungler decides to gank when they never ping or let me know what they are about to do, and when they are going to do it. Usually this puts me in a bind because they decide to dive in when I am in the worst possible position to back them up.

People that don't see their jungler coming are the same people that complain that they get no mias. Watch the map ffs.

I jungle, a few things that make or break a gank is;
do we have it warded? if so gank is highly more likely
does the opponent have it warded? if so gank is almost not going to happen. (vision ward [not sight] and your jankle will love you)
awareness, all players in the lane being ganked need to be aware and ready to strike
positioning, let them push as far up as they will before making any aggressive acts as to scare them back.
Targeting~ everyone needs to focus the same toon.

i agree that jungle is the most important role in game since it can help all three lanes. A good jungler should:
1. BUY WARD.
2. keep ganking. Sometimes a small gank will force your opponent to fall back and your teammate can farm and control the lane again. Also the minion's exp will help you reach 6 faster.
3. tell your teammates which lane you are going to gank. For example (gank bot in 1 min), so that they can be prepare and save skills for kills. And of course you have to ping which one you focus.
4. Know your champ advantage period. Early game champ such as lee sin should gank at lv 2 right after red, while other mid game champ such as ww should rush 6.
5. Record the time of all sorts of things. Buff,dragon and baron spawn time, and enemy summoner skill cd.
6. Be a leader. Jungler doesn't require much personal skill. But you need a good sense.

I've played jungle a bunch and I have to say it annoys me to know end that people in lane feel the need for you to instruct them as to everything you are considering doing. If I am running toward your lane or sitting in a bush, prepare for me to gank. If I have to take the time to ping or say "go" that split second could be the difference between taking advantage of the opportunity and winning the fight, simply losing the fight, or getting completely counter-ganked. If the jungler is expected to be able to keep an eye on every lane, each lane can at least keep an eye on the lane and the immediate surrounding area.

I think the tone you have on your post is really negative towards junglers, and you come across as the person that blames jungles for stuff, you should say things i love about my jungler, and say you love when you have a great jungler who pings and lets you know.

GD complains way too much and doesnt say what they like about their teams