Have something to say, and say it as clearly as you can.
That is the only secret of style.
— Matthew Arnold
Understanding what you are presenting requires some effort for the reader. If an assignment is well written the reader can focus completely on understanding the content. If an assignment is poorly written, the reader must use energy just to decipher what you are saying, and may have no energy left to understand the actual scientific discoveries you are presenting. In the case of research reports and other university-level writing, this can have implications for the grade you earn.
While your instructor is the one who will grade your report, you are not writing for your instructor. Write at a level that a student in your class could understand rather than at a level you think will impress your instructor. Write for a peer in the class who did a different experiment than you did. Try to explain the concepts you did not understand before you began your experiment. This is not easy to do.
Rather than writing, "It was found that the enzyme funkiase worked best at 45°C," (impersonal, passive) isn't it much easier to read the phrase "We found that funkiase worked best at 45°C" (personal, active)? Or better yet, omit unnecessary words: "Funkiase worked best at 45°C" (active).
The exception to this is the Materials and Methods section. It is not always possible to use active voice in this section.
A paragraph should make a single complete point. The first sentence of the paragraph should summarize the main point of the paragraph. The rest of the paragraph should contain supporting information for the main point. Ideally, the reader should be able to get the gist of what you are saying if they read only the first and last sentences in your paragraph. Incidentally, reading the first and last sentences of a paragraph is also a good strategy for reading journal articles.
In a research report, a paragraph's topic sentence will usually be an important observation or a conclusion. In the results you will present the key trends you observed, so each paragraph should start by stating a clear result. The rest of the paragraph will be used to backup or to expand the result. In the discussion, you will be focusing on what the data means so most paragraphs will start with a conclusion. There are examples of how to do this on the results and discussion pages.
Why use a $20 word, when a $1 word will do?
Verbosity is very common in scientific writing, but that doesn't mean it's the standard you should strive for.
Using non-standard language causes your reader confusion, which in turn weakens your argument. See the List of Common Errors.
You may be tempted to quote passages from your source. If you enclose these passages in quotation marks and include a citation, then you will not be guilty of plagiarism. However, science writers generally don't quote because they are expected to use other scientist's results and ideas, not the original author's words. It is the ideas and results that are important, and we use these to lend credence to our ideas or to compare and contrast with our results. When we rely on quotes, we are not adding any knowledge to the scientific community.
There are three main reasons that students tend to use quotations:
The solution to #1 is to determine how the information fits into your narrative. For example, does it help you explain why this study is important?
The solution to #2 is to remind yourself that in science simple writing is better because complex writing makes it harder to understand the scientific importance of what you are trying to say.
The solution to #3 is to describe your thoughts, hypotheses, or interpretations of the work you are citing rather than just presenting the original author's ideas.
One strategy that might help you with all these problems is to first explain, out loud, to someone unfamiliar with what you are writing what the passage you are using means. Then, explain how this information fits with your study. Once you can explain it out loud, you should find it easier to write it out. If you don't have a willing audience, try recording yourself!
Getting the words on the page is only the first step. Although it is important to get the words down before you forget all the important points you want to make, revising your writing ensures that you are making those points clearly and effectively. The essential component to good revision is time. Let your lab report "sit" for at least a day before revising it. Remember that revision is much more than simply correcting grammatical errors (for more information on how to revise your lab report, see: How do I review my own writing?).
This paper gives tips on how to communicate effectively. Optimizing scholarly communications: 30 tips for writing clearly. 1996. Kenneth L. Knight and Christopher D. Ingersoll. Journal of Athletic Training 210: 209-213.