An Overlord has arrisen from the Tombs! Welcome to the forum!
Here are some tips that might help:
0- get the codex, 1st thing you must do, until then just dont play, you need some required preparation to start playing...
1- get 20 immortals with Gauss Blasters as others said.
2- get 2 NIGHT scythes. Put 10 immortals and a harbinger of the storm with lightning field (Or just "fieldtek", check out their names at the tactica section.), in one of them. Put an Overlord and 5 Shieldguards (Lychguards with shields) in another Night scythe.
3- laugh scornfully as the enemy gets chopped to bits by the scythes and their occupants lol (Question, have you got the rulebook? Did you learn basic rules? If not, LEARN THE RULES BEFORE PLAYING ANY GAME).
4- A monolith would be great to give your army a mobile fortress of destruction.
5- read the fluff, search Necron info on lexicannum, have a look at google pics, get the necron feeling
Now the tricks:
DEATHMARKS! Those guys are great! When they deploy (so choose to deploy 2nd), you pick a unit on the board and even in a transport, and that unit the Deathmarks wound on 2+ in range or in CC (close combat). Now their snipers can both move and fire, but normally always wound on 4+ exept the marked unit (the one you wound on 2+) and on a to-wound roll of a 6 the enemy model auto-looses a wound (Unless it has an invul (invulnerable save) or is in cover).
Now Deathmarks sound good but not kickass enough er?
BUT if you stick a harbinger of dispair with Veil of darkness (Veiltek) then he becomespart of the unit and benefits from its special rules, which means that his weapon ALSO wounds on a 2+ (and check out its rules and see its divine greatness lol).
TRIARCH PRAETORIANS: nah dont take them at all, not worth their points, get Lychguards instead...
LYCHGUARDS: ALWAYS with shields unless you want them to die from a Vindicator shell... but as long as you keep them shielded and in night scythes along with overlords, you are free to smash, stomp and burn (muhaha).
SCYTHES: night ones are great as they begin off-board and enter on 3+ on turn 2 and 3 (automatically on turn 4) and, just because they are NECRON flyers, they can move 36" and disembark troops (aka overlord and lychguards) AND fire their weapon, same with doom one but it is not actually THAT powerful anymore because the anti vehicle job is already covered by Gauss and Stormteks...
STORMTEKS (aka Harbingers of the storm, no wargear): Those little guys come with a 4-shot staff that for every hit, roll a D6 and on 2+ a vehicle looses a "wound" (not actually a wound but a Hull Point, check the rulebook...), so 2 of these guys, supported by 10 Immortals are one of the best AT units in the game( dont forget, always at least 10 Morties (or Immortals, or Imms) in a Night scythe with a Stormtek ).
MONOLITH: Great, tough, and comes from the sky and fires all its weapons at different targets as normal and not only as snap shots!! (check the rulebook). AND they can teleport a unit of, say 10 Imms and a stormtek to kill a vehicle...wow.
ANNIHILATION BARGE: Good when you roll 6s or when there are 2 or 3 firing together, best used at 1000 points games when the enemy cannot easily deal with an armour 13 vehicle. can also be a flyer killer as on 6 the flyer tipically dies horribly...
AEGIS DEFFENCE LINES: Not in the codex but in the rulebook, definitely get them and a Quad gun for killing flyers and to camp Warriors behind to take objectives.
SOLARGAZETEKS (Harbingers of destruction, both items): Those go with the Warriors above, behind deffence lines. they are great at defending and messing up with the enemy shooting...
GHOST ARK: Nice, and the only case in which i would run Warriors, put a Lord with them as the ark can use its special ability on him too!!!
Alright enough, learn to master those comboes first then i can tell you more...