If you are like me and have had extensive bouts with tanks in BF3 and trying to take them out on foot you will know some of the difficulties in this undertaking. One of the most effective depending on placement and the operator of the armor's awareness. I have found that setting a trap for tanks can be a more effective means of not only taking out the armor but as well as lowering you chances of being spotted by infantry on the ground. The best way i have found to make the most of setting a trap is to observe the usual spots that armor will sit and using that to setup your devious little trap. Depending on the area there may be certain directions of entry most armor will move into a area. This can be used to your advantage by placing c4 on a wall or surface that my be driven past that they cannot see the c4 on.
Placing your charges in grass areas that have tree cover do make it more difficult for someone to spot your charges. Have you ever had someone in armor who just sticks to main roads and has a full crew ready to jump out and repair at the first his of a rpg? Study the direction the driver uses and place your c4 in his path and then use your supplies to hide it. depending on the amount of action happening around and just the fact that it is just a supply box in the road the driver may just drive over it letting you take him out. If you are in a squad and you are using a mic you can try to get your squad to help you by placing c4 on the eod bot and blowing it up that way. But of course with the new patch you can just have a squad of engineers ambush armor with their rpg or smaw and if someone has squad expl then you have more than enough rockets to take out armor. In the end you are just playing a video game so don't be frustrated when your tactics fail to work but when these tactics work I know that they put a big smile on my face.