If you're working in the lab outside of the dissecting teams, you'll need your own lab notebook if you don't already have one. There are several formats you can use as far as paper / binding / etc. My suggestion is to start with a pad of quad-ruled paper and a 3-ring binder, available from Biochem Office Supplies or from Office Depot via PurchasePath, and see how that suits you.
There are a lot of different styles of organization and layout that people use for their lab notebooks, but by keeping in mind what they're useful for, and erring on the side of more detail when in doubt, you'll develop your own good system.
Format[]
On each page of your lab notebook, near the top of the page, should be the date. I put it at the top right, and if I start a new day on a page I draw a horizontal line and put the new date in the top right of the new section.
When thinking about what to write, and how much detail to include, remember that the MINIMUM that this should accomplish is to enable you to figure out exactly what you did later on, when (not if) you're trying to figure out what went wrong with some experiment that didn't work. Ideally, you'd like someone else, who might be working long after you've left the lab, to be able to figure out what you did exactly, and also why you did it. If it isn't immediately plain why you're doing the steps or experiments on a page, a note to explain this is very helpful later.
Examples of what to include[]
You should include a hard copy of all pictures of gels, and all pictures of plates and tetrads, clearly labeled. For very large data sets like long sequencing runs or microarray data, at a minimum list the file names including the directory, both on your local copy and on the copy you should upload to your folder in the FTP server for anything important.
When you do a calculation on how much water to add to dilute something, or on how much of each reagent to add to set up a reaction like a PCR , always show this in your lab book to help you find any sources of error later on.
When adding a series of reagents to a complex reaction, a checklist that can be ticked off is useful in organizing your experiment and in detecting anything you may have left out if things don't work.
For PCRs, at a minimum also list the name of the program you used and which machine the program is saved on.
For kits and enzymes, there is usually a lot number printed on them, and this is helpful to note whenever you use them for anything.