First of all, you need to have a very good antivirus software in your laptop. There are many antivirus programmes on the internet e.g. Norton, ESET, Kaspersky, AVG, Avira, McAfee and F-secure, you can download any of them. After downloading the antivirus of your choice, install it on your laptop. If you have downloaded an old version, you must update it. Besides, you must keep the auto protection on to get the maximum security against malware.
You should know that updating your antivirus is not enough and you have to update your Windows too. Microsoft releases security update codes which help in safeguarding the Windows from potential threats.
If you have to transfer data into your laptop from your USB, you should scan it first, just after connecting it to your laptop (before opening it).
You should avoid transferring your files from your memory card to your laptop. You can transfer those files after writing them on a CD. However, if you still want to use the memory card, scan it well before opening it on your laptop.
You must use secure network to browse the internet. Moreover, you should not open unreliable websites. In addition, you should know that many viruses come to your system from your emails. Therefore, you must only open files or links which have been sent to you from your own contacts.
Always keep your laptop password protected so that no one can access your system without your permission.