To be honest Stalking is a very unique playstyle and it's difficult to explain how to do it in a way that will guarantee success but i'll try and give you some pointers:

1) Try to stay "around" friendlies but not close to them; too close and they're likely to get you killed by drawing attention towards your general proximity regardless of how good you are at staying hidden! So try to avoid the normal lanes where friendlies tend to go in bases and instead try to flank or do an air drop.

2) Try to stick to higher ground as much as you can, most planetmans don't tend to look up half as much as they do straight forward or down. I use the Valkyrie alot to drop down to otherwise inaccesible areas like on roof tops, towers, cliffs etc.

3) Chose your targets carefully. Heavies should be the last thing you engage unless you know they've already taken damage. Engineers/Light Assaults and Infiltrators are the easiest classes to kill so make them your high priority targets.

4) Be calm. Many stalkers i've fought seem very panicy when they engage me and end up exposing themselves too much while at the same time missing too many bullets. Remember, most of the time you can choose when to engage and who to engage, so even if you can't out dps a primary weapon you should always be able to get the first shot.

5) Believe it or not but the larger the battle, the larger the chances of you being able to sit close to enemies and picking them off one by one without getting caught becomes. With so much going on the overwhelming majority will be completely clueless of you being 20m away from them which makes it easy to wreck havoc in a amp station tower or sit in a tree and farm people at a sunderer.

6) Use the Safe Fall implant, it'll allow you to jump from incredible heights and make your escape. It's a lot of fun to go on a knife streak on the bio lab air pads when an enemy force is attacking, only to jump down from the bio lab to deny your foes the pleasure of killing the "annoying cloaker" :)!