To consult the I Ching effectively (as with any form of divination) you will need to be in a relaxed state and free from intruding thoughts and worries. You must make sure your mind is clear if you want to receive the wisdom of the I Ching.
Once you have reached this state through meditation (or whatever works for you) then you need to clearly formulate your question making sure that it is not too complexly phrased. If your question is complex then it would be better to break it up into component parts and consult the I Ching separately for each part, which will give you a much more effective answer.
You should only attempt one question at a time otherwise you may not get an accurate answer. Once you have had a question answered by the hexagrams of the I Ching you can go onto another question or another part of a question, whichever is applicable.
The simplest method of consultation is to use a coin. Take the coin in your left hand and as you state your question out loud toss the coin and let it fall to the ground. Traditionally "heads" is considered yang and "tails" yin.
If your toss produces yang draw a short unbroken line on a piece of paper. If your toss produces yin then draw a short broken line. This line forms the base of the hexagram that will be the answer to your question. Continue to think of your question and toss the coin again. And again draw the resulting line making sure that it goes above the first line.
Continue to think of your question and toss the coin until you have drawn six lines. The last line you drew should be the very top one. The six lines you now have represent the hexagram that will answer your question. Now that you have you hexagram you can go on to interpret its meaning.