General notes:

Don't build glass cannons. EVER... unless you have ghost/cleanse/flash and a champ ability that is a natural escape and the enemy lacks solid CC and you're a ranged champ. Building merc treads will always be the pro choice.

There are a a couple diff strategies that 5man premades can run, I'll go over basic strategies below.

AoE (Nunu, Galio, Amumu, Kat, Panth, Vlad, etc)
They all have a couple things in common, they all are magic damage based & they all have to have a team fight to be effective. This is easy to deal with, build Banshee's and/or Quick silver sash and don't team fight. Just split push, its pretty easy to do. They are all also very burst damage based, so if you survive the first 5ish seconds, you can easily DPS them down.

Global (Panth, TF, Shen, Wangplank)
This one is a little more annoying since they have great split pushing abilities, the easiest way to deal with this is grouping up and trying to knock them down fast.
Early Game vs global: If one of them leaves your lane for a gank, push hard since they can't get back all that fast. Put some hurt on their towers and they'll think twice about leaving for a gank if you kill their tower.
Late Game vs global: Run as a team and push as a team and ward, they will want their tanks/nonglobal to initiate and then they ulti in for position, this is easy, burst down the ones near before they have a chance, OR if they do manage to all ulti in, pick out the weakest/squishiest chamap (Panth or TF)

Invisible (Eve, Shaco, Twitch)
Don't push your lane so they can get you. If they spend all their time invisible trying to get ganks, that is how they level and get gold, if you deny them that opportunity, that will hurt them later in the game, also invis champs tend to suck late game. They are easily countered by oracles. Have two or 3 on your team and they are useless.

All Tanks/ tanky dps
This one is a bit more difficult since the enemy is relatively difficult to kill, everyone build banshee's veil since all tanks are burst based and build madreds if they have high HP and be sure to build Void staff or last whisper to melt through armor/MR and if the game goes late, build a GA and they'll have issues trying to dps you down.

early game laning strategy
Don't waste your mana since both Lux and Blitz are very Mana intensive, save your mana for grab snare combos when you can land max damage. Pretty much either Lux snares so blitz has an easy grab or the other way around. neither of you can really DPS them so the best way to do it, is to harrass them to about half health, and then grab/snare/ehxuast ignite dps for the kill and always go for the easiest kill i.e. the one that can't heal or the one that doesn't have any health pots left.

Also, every time you base, buy a ward. just do it and ward your river, if you get ganked from their jungle because you don't have a ward... that is pro noob status right there. wards get you kills and keep you getting from killed.

Starting items: get a mana crystal and 2 health pots, don't get a mana pot. staying in lane and getting xp and last hitting is more important than getting mana and losing on health. Also, if you look at the defensive mastery tree, spirit of strength boosts your HP regen by the amount of mana you have thus keeping you in lane longer than the enemy. Secondly, rush that catalyst, it is the best laning item in the game and waaay better than tear of the goddess, once you get this (around lvl 5-7) you can stay in lane until we have to group up. It will heal you and give you mana every time you level up.

Lux
Definitely go with the build path above, you'll benifit yourself and the team more than rushing an archangels. it balances CDR, survivability/support for the whole team as well as good late game damage. Getting soul shroud and having cataylst will give you all the mana you need. Boots are situational depending on what the enemy team has but I suggest either merc treads, swift boots or sorc boots. Lux's AP ratios are just ok imo and she benifits more from CDR so she can spam her snare and shield. Be sure to land your shield on Morde and Olaf when it comes to team battles. Suuuper important to protect them. Even with full CDR Lux can only shoot stuff off every 5 seconds or so, so just stand in the back and provide damage and traps and shields when you can.

Blitz
Its your job during team fights to disrupt their squishies and CC champs with grabs, punch ups and your ulti.

ignite = ulti combo OP roflroflrofl win.

Do your think, get in there do damage and don't die. EZ kills.

you should rush starks fervor, I think its more beneficial than ghostblade. the lifesteal and AS just synergize more with olaf than ghostblad imo and the AS and life steal aura will definitely help morde, blitz and Corki.

After that, just stack health with Armor/MR items and your E will be enough to deal damage on the enemy team.