Also, stay out of close range with a viking. Apart from that, good luck.

The railgun is a powerful turret, meaning killstealing is very simple. Just wait for a enemy tank to recive damage from one of your team-mates (preferably not a friend) and shoot them. Bare in mind the reload time, approximitly 5 seconds. viking is a good hull to go with railgun, as iot is fast enough to zip in and out of cover, while not shedding off to much armour like the wasp or hornet. Hunter also works well. I advise a anti-close range paint, to protect against firebird/twins etc.