Your research notebook is the only written record of your experiments, observations, and general progress. Without it, you cannot summarize your work in a final written report; indeed, you cannot even prove that you have spent all that time in the lab! Treat your notebook as the very valuable property that it is. Do not take it home, unless you need it to write your final report.
Each new reaction should be recorded on a new page of the notebook. This is true even if you have done the reaction before. The notebook page heading should still appear as the sample below.
This is an important requirement - get into good habits right at the beginning!
Below is a sample heading of a notebook page as it should appear prior to beginning laboratory work. If a reagent is a liquid, its density should be noted right after its name. The number in brackets under each molecule is its molecular weight.
ref. Hayward, R.C. et al. J. Chem. Ed. 1984, 512.
(date) Description of glassware setup and then of reaction, as it is being run, begin here.
When the experiment is over, write a short (one line) conclusion - this is especially important if the reaction did not run as intended. But, in any case, you should note the yield (of course), several IR absorptions (and what they mean), NMR signals (ditto), and TLC data. Don't just leave the experiment notes hanging - people need to be able to look at your book 10 years hence and immediately know the story of every reaction you ran.
ALSO - when you finish an experiment, you need to get another group member to look over the writeup in your notebook - to be sure you've adhered to the directives in the above paragraph. When you are asked to do this, please take it seriously - don't just scribble your name after a cursory glance. If I find a book with poorly written documentation, incomplete writeups, etc., it's the signer I'll be looking for, not the researcher!
1In other words, please do it!!!