Irelia is a rather flexible top laner whose draw back is a bit of an unforgiving first few levels. Before I continue on I want to emphasis that the answer(s) provided before me are correct in their entirety (trade with your allies to accomplish the best possible pregame advantage is a HUGE asset to winning top lane). However, there are additional factors that you can influence to alter the course of top lane most notably duo queue, especially if the person you are queuing with is almost the same elo as you this will naturally force you into a lower position in the roaster, thereby levitating some of the pressure of first pick. Of course this certainly provides its own fall back in such regard as that you might not longer "get top." The secondary option is to queue with someone who has a noticeably lower elo then you (>30), whereby you'll be guaranteed one of the first spots on the team and your teammate will be forced into the lower positions, from there you can have an arranged trade which will be very hard to challenge (we all know half of LoL believes pick order determines role and the other half believes calling does). If you aren't interested in going duo queue then you next best option is to influence your jungler's choice, seeing how Irelia is weak at low levels forcing the jungler into a lee sin or xin zhao role will naturally provide you with some much needed early cover, especially if you sell them on the idea of ganking top by being friendly and suggesting they should get the kill. Beyond the team work elements that everyone has been discussing there are some very fundamental build choices that radically alter the way the game unfolds, an early cloth armor can easily protect you for the first 5 lvls against even the most frustrating harrassers (you'll need to practice the trades but you'll see with proper minion positioning you should come out ahead). The draw back here is that you'll need to fill your build with more gp5 items since you'll naturally find yourself missing whatever alternative item you normally would've had (probably boots). This has a net aggregated effect that your lane WILL span into the 18 minute 20 minutes phase before you have your trinity secured. Furthermore, if you get out of position or your enemy decides not only to counter you but also to get jungle support, and you die then you'll find that the alterations in your build to levitate early failings on irelia's survivability will come hit you rather hard in terms of "perception of usefulness" with which I mean you'll feel weaker for longer. Having player over 3000 games, I can tell you the solution for the jungle problem is wards and a willingness to give up CS and lvls in exchange for surviving (people frequently extend themselves for the margin minion, you just want that one minion and then you'll run back to base, DONT DO IT). Furthermore, get your jungle to give up elements of his jungle (I once had a lee sin give me control over wraiths and golemns when I was top Irelia, I went from being 0/3 to being 11/5 that game because I got farmed up) if you DO fall behind. Lastly, if you are committed to irelia then you'll need to view her as what she. She is a character who can make a lot of different things work for her (AD, AS, Armor, ArmorPen, MS, etc.). You need to devise MULTIPLE rune pages depending on what kind of opponent you are facing (if you are fighting a vlad you'll want the early MR, if you are facing a Riven you'd be much better served using those blues on flat mana or some alternative). Dynamic rune pages and masteries can radically change the way irelia unfolds during the game (I know we all want to go all or nothing to an extend and invest in the late game everything, but that isn't realistic if you open yourself to hard counters), in effect you'll want to test to see what works best if you are especially clever you can use something like lolking.com to see what kind of setup they are running (if they are running tons of armor then get no armorpen, if they have no armor then run armor penn, etc.) or at least what kind of setup they are likely to run. In the ending if you are REALLY set on playing Irelia and all else be damned there is a GREAT deal you can do to throw the game back into your favor, especially since flexibility like this will confuse most people since they are expecting the "meta ready" Irelia.
In conclusion: greatest is best achieved by doing ALL the things I suggested. At the end of the day you need to devise a viable plan for how to patch the early game, because no one is save from you come lvl 9, unless you already fell behind! (that rhymed)