Play more norms before heading into ranked.
Have two complete tier 3 rune pages, one ap and one ad.
Have 1-3 champions in EACH role that you know very well. You should have at least one that you know like that back of your own hand. One that doesn't take much thought to play, and one back up in case that champion gets banned.
You should also take time to focus on mechanics such as last hitting, proper positioning, warding, ganking (for jungling and roaming) as well as taking objectives. Familiarize yourself with the timers for buffs, drag and baron and a variety of other things. These are all incredibly important things for ranked play.