When you act with others, face to face, you can hear how they read their lines, and adjust your own accordingly. The director can hear you and give immediate feedback. When you voice act remotely, as most amateur VAs do, you don't have this advantage. It is very easy to record lines that make no sense when combined with others' lines, or mistake the director's intent. Many amateur producers will go ahead and mix your lines together anyway, resulting in scenes where the characters are apparently not listening to one another. Even if they do ask for changes, that takes extra time and can get annoying to all parties.
To minimize the issue, many producers ask their VAs to submit multiple takes (usually three) for each line. The mixer can then select the best take for the scene, or may combine part of one take with part of another. Of course, it defeats the purpose if the three takes are all basically the same, so it is important for VAs to be able to come up with different ways of reading each line.
Coming up with a single interpretation of a line is usually easy; you get an idea of your character and the situation, and a meaning will often seem obvious. Most lines, though, will have more than one possible reading, and just reading through will often suggest others to you. A common trap is to read the line once, read it a second time differently, and then try to do it again - but have the third reading be essentially the same as the first, because that is the most obvious reading different from the one you just read. Here are some suggestions for ways to find additional readings.
A simple change in emphasis can completely alter the meaning of a sentence. For example:
I'm not tired (you may be, but I'm not) I'm not tired (I could keep going for hours more) I'm not tired (I'm just bored)
Think of different ways a character could feel about what they're saying. "I could be in love you" could be speculative, it could be shy and hesitant, it could be eager. "That seems hard" could be satisfied that poured cement has finally set, or it could be daunted at the difficulty of a proposed task. If a character sounds happy when saying, "I slept until ten," it could mean that he finally got a decent night's rest, while a panicky reading suggests that he overslept and missed an important appointment.
Ultimately, doing multiple readings for a line is both a discipline (forcing yourself to do it when sending in lines) and a skill that comes with practice. To get some practice, pick up any script and just go through the lines, one by one, trying to find a reading that seems completely non-obvious. Most of them will probably make no sense in the context of the scene, but sometimes you will find new depths in the character or possibly completely different interpretations of the scene. It is one of the best ways to take a chance and create extra energy for a character. Don't be shy,