There are a lot of different sub-areas in biology to consider. It will be impossible to specialize in them all. So you should consider what specialty you'd prefer to go into (e.g. molecular biology, genetics, etc.). Take a few courses that go into some of the specialties and find the one that you like the most.
To also become very adept you'll want to consider approaching some of your professors to do some extracurricular laboratory research (for either academic credit, pay, or experience). This will help you tremendously in acquiring the lab skills needed to be a great biologist.
That being said the biology field itself is flooded as with most other fields. In order to have a successful career and to have an easier time of getting there I would suggest combining your pursuit of biology with something in the chemical engineering or genetic engineering fields. If you go the engineering route you will have a much easier time in obtaining a job (and a lot more money than just a general biologist). If not then you'll definitely want to consider attaining your PhD in order to be competitive in the marketplace.
Additionally, talk with your professors. All of them. Utilize their office hours and ask for their personal advice and what they would do in your position.
Best of luck,