in addition to Hena's suggestion, I would say that epic isn't so much about list building as the 28mm scale GW games, and some armies (eldar for example) are a lot less forgiving to a beginner (they also have multiple distinct builds, there isn't really a 'generic, take all comers' eldar list in my experience)

there is a great website: here with an army builder for all the major lists so you can play around with different builds very quickly and all the sums are done for you

Additionally there are certain builds which are common in tournaments (space marines with thunderhawks and landing craft springs to mind) but less so in 'friendly' play

I would recommend something along the following for IG (my main army) the points may need tweaking....

Reg HQ with flak - for nabbing objectives and the important SC re-roll
infantry company with flak - garrison an objective, fire support could be added here
tank/heavy tank company with flak - some armour and solid firepower, I prefer Superheavies in this role, but some like Russes, it's up to you

artillery battery - many prefer manticores for the extra BP, but all 3 are sound choices (I love bombards for hitting enemy garrisons)
artillery battery
hydra battery
sentinels - for guarding your artillery or vulnerable stuff against teleporters
deathstrikes/shadowsword - deathstrikes are more powerful, but one shot, a shadowsword can hang around making a nuisance of itself

warhound titan - speedy and hard hitting, they are quite fragile though, try to keep them alive and within 75cm of your opponent's blitz on turn 3
warhound titan
thunderbolts - solid ground attackers and interceptors

you can then tweak it to suit your tastes and playstyle, you might want to add stormtroopers in valkyries and rough riders to go all-out assault, just bear in mind that guard struggle to keep a high activation count so always aim for a minimum of 9, you can gain an extra activation by downgrading your Reg HQ to a standard mechanised company and buying a sentinel platoon with the spare points....