I'm pretty new to the whole PvP scene and one thing that I'm having trouble grasping is the ambush. What I'm noticing is during the late stages of the game whole teams will float through the jungle and ambush other players

Normally I know to just run away when I see them coming and that works sometimes. What I'm experiencing though is when players like Jax, Garen, Lux, Fiddles, and the yeti man (don't know his name) ambush you and slow/stun you. It's lethal and as I'm leveling up I'm finding that some teams solely do this and do it well

What suggestions do you have for n00bs like me who can't seem to defend against it

wards

Helps if you have people on your team (yourself included) warding where you feel the next fight is going to happen.

If you have no vision at all though check brush with skill shots like ezreal's mystic shot or anivia's wall.

To newer players wards might seem like they cost a lot and they do if they aren't used effectively but they can be used to gain advantages over the other team and allow you to set up kills easier. Supports should ward heavily at choke points(don't try to blanket the map). Warding things like bottom river bush, top river bush, dragon, baron(later on) and buffs are good ideas. These can lead to kills/ganks if your team has good awareness of the map.

Examples: I use a vision ward in the bush near the enemy blue buff about 30 seconds before it should respawns. Knowing that their jungler or mid will want to grab it, you can organize a gank in advance or as it is happening(If you do not know appoximate timings)

I am playing support and I see the enemy team ward bottom river bush so I counter ward bottom river bush to return the gold cost and deny them vision and well as protect from ganks(Note that some characters like nocturne, katarina and malphite still have the ability to gank efficiently despite having warded).

Eventually, you'll want to get used to mentally tracking the position of the five enemies at any and every moment of the game. When someone disappears, you want to notice it, then ask yourself how long it would take them to gank you out of the shadows, assuming they started running full speed straight towards yourself. And then make sure you're near a tower before the hypothetical gank takes place.

In the mean time, just do a check of who's on the enemy team. If it's someone with a jump or stealth, try sticking a little closer to your teammates while roaming about.

And lastly, before going into any brush--and I do mean any brush at all--check your minimap, or press tab. If there's any opponents not visible on the map, assume they are all piled up in there, waiting specifically for you.