Train

Train is a fairly complicated map, not only is it dark and there are a lot of places to hide, it has a lot of choke points, it’s easy to be dead before you see someone.

Terrorists:

There are 5 points of entry for the terrorists on this map, these are through vines, through the mid connector, through the ladder room, these three will get you to the A site. The other two entry points are lower ramp and top ramp inside which will get you through into B site.

Vines:

Vines is hard to work as a T because there are many ways for it to be held, it can be held very aggressively, very defensively or inbetween. Aggressive holds of vines would be someone holding from in the actual vines room, on the barrels more often then not. Defensive is holding from way back on the CT spawn stairs. The hold inbetween these is usually a cross fire, one will be on the left and one will be on the right, with a crossfire set up. The best way to attack vines is by using a flash on either the right or left, and then flash the other way as hard as you can and rush out together.

Mid Connector:

You will want to send an AWP into Mid connector to pick outside, although there are many spots that the CT AWP could be, if you play it smart from Mid Connector you can generally get a pick or two without having to even battle the CT AWP.

Ladder Room:

A very small room which is very hard to get out of if you are not careful, either held close up by an M4, or way back at the bomb train by an AWP, getting down the ladder is tricky, however once in, a couple of well placed smokes and flashes will get you out.
Tip: Do not rush ladder room as a team, it is virtual suicide.

Lower and Top Ramp:

The reason I say these together is because you will more often than not split up between these two as a full team, a couple of well placed smokes down the lower ramp and up on the top ramp will give you the cover needed from their AWPs, throw lots of flashes deep into the site and check the trains close up, plant the bomb and hide!
Tip for train: I would suggest if you want to rush hard to either rush down the lower ramp with flashes to the back of site, or rush out of mid connector everyone throwing a grenade in to the CT connector. Rushing vines is harder, but use flashes and you should be right.

Counter-Terrorists:

The most common hold for CT on this map is having 2 inside (one watching top ramp, one watching lower ramp), 1 watching ladder room, 1 watching vines and 1 watching mid connector. Remember to use the trains to your advantage and also the dark spots with your dark uniforms!
If you have someone who is able to hold inside all alone, this is fantastic because having 4 players outside will help you a lot more because outside is usually worked a lot more than inside.