Tactics Question

So I tend to play with my group of buddies who generally run Necrons, Orcs, and Dark Angels. Now I usually can hold my own, but I still have issues of getting to them, harming them, or surviving. General tips are really appreciated.

Can you give us an idea of the points value of the games? Rough army lists?

Personally as I often play my brothers Space Pups . The advice I would give is out manoeuvre them and use your army like a scalpel. Use cover where you can with everyone.I generally play vs 2 long fang packs and a Predator at high point games.

Try and set up with double saves if longevity is a problem. Consider a few cheap haems and min sized wrack squads vs one expensive archon so that you can caddy pain tokens off the bat.
Use nightshields and tease your opponent by pre-measuring and dancing out of range of the 24" shots. Focus on removing the longer range threats first. If mobs get within 12", boost away from them and sacrifice shooting for a flat out move. You cannot afford losses! Effectively, you become an itch they can't scratch, which become a wound and sooner or later they will bleed out.
Watch a video about how the Komodo Dragon hunts. Be patient like that SOB. My bad run with DE is due to me thinking I can smash people in any assault. Smashing people in a well timed assault works better eg when I can bring 3x5 wyches to bear on 5 SM, the odds are in my favour!

The Ork Player tends to bring 20 boys in trucks, along with a large amount of lootas. Can't say much for the necron, been awhile since I've played him, the Dark Angels player loves his termies and deepstriking them. Thanks for the advice so far.