I think you mean before the stalest meta of 1-1-2-jungler? I mean, there was a different meta back then, but it was a meta none the less.
Well, for starters ADC went mid. Usually had either 2 duo lanes, unless you had a jungle champion who was played by a summoner with jungle runes (yeah, S1 jungle was that beast. No little boys, if you survived the jungle to gank a lane with even half an HP bar, your team loved you.).
The duo lanes varied, but usually you would either find a tank/bruiser and a Mage/assassin. Some combination of Damage and CC. If it was a solo lane, they either A) had to be capable of soloing vs 2 people, or B)waited it out under tower until they could out level their lane opponents.
Jungle was brutal, only a select few could even do it, and you needed the right runes and masteries to survive. You completed your lap around the jungle, and the best junglers would be safer picks that didn't take a year in the jungle. Warwick was actually a top pick, beleive it or not.
Mid lane ADC was interesting, as the top picks were Ashe, for her safety from ganks, and Tristana, for her huge leap to safety or to ensure a successful gank. Kogmaw came in third, as his range was long enough to compete. Never been a lot of picks for ADC, but at that time the pool was exceptionally tiny. TF, Urgot, and Teemo were considered ADC's back then as well.
As far as any other differences, Warding was no where near as prevalent except at the highest tiers of the game. The community was way more lax, and since the tribunal hadn't happened yet, the language was not rated PG-13. That said, it was much more fun, as you could say and do alot of harmless but funny things that would get you banned nowadays. Everyone had thicker skin, as for a report to do anything, you had to manually put it through player support. While it may sound like I'm moping, the fact of the matter is that the Tribunal needed to happen, so even if the community pushed for a cleaner game to a little excess, it's still better than MS Rammus/Yi running down mid every game you found a 2 year old who didn't get the role he wanted.
As for team comps, the favored comp was Heal/poke comps, over all-ins. As a result, Taric and Janna were exceptionally popular in terms of support (back then, Taric's ult was a toggled AoE heal for his team, that gobbled his mana bar within seconds.) Mages that had good poke were usually favored, however AP gragas still hadn't really been recognized fully, so more along the lines of Heimer (oh god was he OP back then, Nades affected towers yo, and if you have problem with his turrets now imagine 7 with no lazars but double the damage loaded into autos. Oh, and the turrets were fairly tanky, and had better range, and evolved to have extra onhit effects.), Nidalee, and other such pokey and sustainy champs.