it obviously varies a great deal between children and you do things when they are ready not by a set time table but roughly...
talking,first words around a year
crawling, from about six months
tummy time, i think you could start now, just not for very long and keeping an eye in case of distress
potty training, usually from about two years, but huge variation on this one, basically when they are ready
weaning, guidelines were 4 months, then six, they might have changed again, big debating point this one! I did my three at about 4 months but this would be totally unacceptable for some parents, again depends if you feel child is ready.
Google baby milestones and you'll get loads of info.