Before asking the oracle, we can ask ourselves how could we answer for the oracle, by using only hexagrams and lines. It can also be useful to ask ourself why we question the oracle.
For example, if I ask you What is the day today?, can you answer me with an hexagram and lines? If I ask you Have you practiced bicycle or football?, can you answer? If I ask you again When do you plan to go on vacation? can you answer with hexagrams and lines? If you can't, then when you ask similar questions to the oracle, your chances to understand the answer are diminished. However, the oracle masters perfectly the I Ching's art and can sometimes find unexpected answers.
But if I ask you Are we Monday?, you can find an hexagram and lines to answer me. If I ask you Have you practiced bicycle? then Have you practiced football?, you can also find answers. Finally if I ask you Are you going on vacation this month?, you can still answer me with an hexagram and lines (you could for example tell me that you are going later with the line 4 of the hexagram 54 and if you are coming back from vacation with the hexagram 24 without lines) . It is thus necessary to make an effort of concentration, not because the oracle would not understand our question, but because we want to be able to understand the answer.
Some specialists will recommend only asking personal questions. This is a well-intentioned approach, because we don't interfere in other's business by doing that. I have consulted the oracle about this, which has answered( 14,5): All are accepted but one will move away from those who claim too much. When you receive advices about the best way to practice the I Ching, if you have a doubt, consult the oracle, and nobody else, about it.