S.M.
One thing that worked for us was for the toddler to put on shows for the baby -- singing shows, dancing shows, even air shows with toy airplanes, car shows, train shows, etc. I would sit with the baby and ask for a show, and tell my toddler that even if the baby doesn't smile or laugh or watch (if too little), she is still learning and listening. When my baby was a little bigger, these shows were a great way for my toddler to get extra attention (from me AND baby) during those times when my baby was very demanding of my attention (i.e. eating every tiny thing on the floor, etc.)
One thing that I learned was to anticipate when I would be giving my baby extra attention, and to try to get down an interesting and unusual toy (best were puzzles, train sets, great big blocks, and tiny dolls) just before I disappeared to nurse or change a diaper. And I would bring a few books to serve as one final level of distraction next to me in case the interest in the toy didn't last long enough. I think it's also useful to discuss envy -- that feeling is so strong in toddlers! Also, reading is great -- there are lots of books that babies and toddlers can enjoy listening to together (I have lists if you are interested!).