Locking in with the drummer does not add "punch" to the band! It simply means playing tightly together with the drummer so as to achieve the desired groove and feel for the song/tune. I think we have to be really careful with words we use to describe things in the forum because we can create misleading info for beginners.
The best way to improve is to listen to CDs and focus on first learning the various basic grooves for various styles such as Rock, Pop, Funk, Jazz, Afro-Cuban, Brazilian etc. When you learn, dun just learn to play the notes, but try to go deeper...For example: iversion763 said-
"hmm... lock in with the bass drum, i think he means when the drummer hits the bass drum, it's a dull "boom". the simple rule of thumb of playing bass is playing a note everytime the drummer kicks the bass drum, which will emphasise the "boom" and make it sound solid and accented."
Which is the basic idea, but to go deeper is to listen to how long your individual notes should be. Should your first or second note be short or long? If short, how short, if long how long? All these contribute to playing a good tight groove.
These are just the bare basics, to really improve, you'll need proper guidance from a professional bassist. Also,
www.themusiclab.com.sg provides band performance courses which is most valuable in fixing these problems too. The band directors are all current professional performing musicians and they'll teach you all you need to know to perform certain styles well in a band context.
Good Luck!