I play orks and still have good results with them, even against necrons flyer spam. The backbone of the army should be, as stated by rabidsnail12, lots of boys! I’d also note that orks should always be kept cheap to achieve this. Here’s my personal guide to Orks:
– Ghazghkull is great but in smaller games I’d save points by taking a mini-Ghaz (Ork Warboss, Mega-Armour, Cybork, Attack Squig). There’s your warlord and he can be accompanied by a squad of TROOP mega-nobs; they all move 6 inches in 6th edition so are more reliable, they have that valuable 2+ save and can take combi-weapons (although I’d save the points).
– I try to take a biker Warboss for the second slot. A toughness 6, strength 10 AP2, fast moving unit with a 4+ cover save in the open (with the option for cybork) is a great tank hunter! Can be hidden in a biker squad (cheap) for abalative wounds or troop Nob bikers if you can spare the points but can go solo with good use of LOS blocking.
– Boys always thirty, always power claw/bosspole Nob. I tend to take shootas now because volume of shots is often better than one more attack and the overwatch potential (although unfluffy) is moreoften a better choice than charging. NEVER rokkit launchas, waste of a turn pointing ork boys at vehicles, but big shootas fit nicely. Often in the event of a challenge, I refuse it to save the claw. Your boys have numbers and enough attacks to cope without it. Save it for monsterous creatures/vehicles that CAN’T pick on the nob by swamping it with boys. I have used this to hold off (and eventully kill) a tomb stalker to prevent it eating my other, more valuable units. Remember: boys are cheap and (should be) plentiful!
– Deffkoptas, better than buggies but i run them as solo nuisances/last turn contesters. Rokkits ARE best 😀
– Dakkajet, only flier I bother with. HUGE amounts of dakka available but fragile when against other fliers/high strength skyfire.
– Now, onto the golden boys. Lootas! Lootas, lootas, lootas! Always take Lootas!!! Orks begin will a low BS so their weapons often have a high rate of fire to compensate. This means orks excel at snapfiring and none moreso than Lootas. Snapfiring with their sheer amount of shots means they can be more mobile than in 5th edition AND, the clincher, they are great anti-flier units! Note: don’t bother downgrading a boy to a mekboy. Shorter range and less shots (that could kill him) make it worthless here.
– Aegis defence line is useful for holding the midfield but you should take gretchins for that turret. Best ballistic skill of the army, but thats not saying much.
– For cheap heavy support you can take big guns: I like cannons for direct fire, some players prefer lobbas for hiding out of sight. Just don’t even bother with Zzap guns…
– Battlewagons are great, fairly cheap AV14. I take them as dedicated transports when needed (better than trucks, always) with a deff-rolla and red paint job. Grot-riggers and a big shoota are cheap so worth taking, just in case.

By no means is this a comprehensive guide as there are units I haven’t mentioned because, frankly, I just don’t use them. That does not mean they are bad units (although Kommandos now are) but I can build a great army using everything mentioned above. If you are still reading by this point, thanks for bothering!