By using smoke you bring attention to the fact that you are up to something
To remain unseen first be aware of what is around to give extra cover, what the wind direction may do and ensure you do not use just one smoke
(Ever seen someone throw one smoke grenade and have everyone just look at it, if there is any depth to the smoke the opposition shoot into it and then it clears up. A few minutes later someone may throw another)
Throw multiple smokes, or even better get a few people to throw smoke
(To get a decent amount of smoke on a field you want about 3 standard paintball smokes, there are new paintball smoke grenades out which put out around the same as 3 standard ones)
This increases the amount of smoke and also spaces out the thicker elements
There is no longer one thick element of smoke which could cover you but attracts fire
If there is no wind then the smoke will hang for you, if there is a mild breeze it may make 'random' clouds
Ideally make the most of it. Move as if it is any other form of cover, go from point to point. Don't hang around, but do allow the smoke to gather a little
Watch and listen for the opposition- are they watching the smoke or randomly shooting into the smoke
Don't run screaming and shooting into the smoke - they may not see you but can hear you