The I Ching uses symbolic language to communicate its messages. Part of it can be understood on an intuitive basis, and part of it is explained in the commentaries. Part of it is under constant debate among experts, and not without controversy, and part of it is unexplained altogether.
I'm not even an expert, so what can I say. I suggest you rely on intuition and such explanations as are already provided for. Moreover, general explanations may miss the point: if they were infallible, why use symbolism? There are, however, symbolic expressions that appear frequently and may be explained easily. Here is an arbitrary selection in a random order:

  • It will be advantageous to see (meet, meet with) the great man.

You're supposed to look for spiritual guidance, but not necessarily outside yourself. If you turn your light inward, you will see tendencies towards love, hate, trust and treason, your desires, hopes, fears and insecurities. If you don't know what you want, your demons will, and their course and objectives will seldom match yours. Here lies the source of 'repentance and regret'.
If your darker tendencies call, it will take a great man to avoid, at the same time, denial of them and acting on them.

  • It will be advantageous to cross the great stream.

The time is right for action on a larger scale. It doesn't necessarily imply travel, but of course it doesn't exclude it either. The motive power of the action may be both to obtain good or to escape evil.

  • There will be advantage in appointing feudal princes.

Here you are advised to rely on people you can trust. You can find such people by being one. The hierarchic implications are non-essential and may or may not apply.

  • The king goes to his ancestral temple.

The king goes to his ancestral temple, there to meet with the spirits of his ancestors. Those spirits were present then as they are now. Paying your respects keeps you in touch with them as well as yourself.

  • We see dense clouds, but no rain, coming from our western borders.

Rain in China usually comes from the east or southeast. Dense clouds coming from the west are rather exceptional. Their bringing no rain indicates a situation of impressive but impotent manifestation. It may be a plan which will not be carried out, a promise that will be broken, a threat that will take no effect, or anything else in that line.

  • Advantageousness will be seen in his getting friends in the southwest, and losing friends in the northeast.

This is a line from the judgement in K'un, and it has a special significance in relation to the Inner World Arrangement of the trigrams.
In this arrangement K'un occupies the place in the southwest (remember south is the top-side), while the northeast is occupied by the yang trigram Ken.

It is an advice to the subject to seek others of the same nature and inclination.

Similar lines can be found, outside this context, throughout the I. Generally speaking, the south is the region of warmth and companionship, the north that of cold and isolation, and the general advise to the subject is to seek company.

  • In seven days comes his return.
    In the eighth month there will be evil.

Seven is the number of the younger yang, eighth of the younger yin, thus the numbers indicate the approach of, or a tendency towards, order or chaos respectively.
In Chinese astrologly, the eighth month is September. The hexagram connected with it is Kuan in which the yin forces have already taken over most of the hexagram.
Other frequent references to periods of time, three years and ten years in particular, do not seem to indicate more than a long or a very long time respectively.