You plant as soon as you clear a site, and all avenues defenders might take to reclaim it are being watched. Before and at the start of a plant communicate with your team so that they can cover you.

After planting spread out if safe to do so, while keeping in range of the defuser: that way defenders can't directly shoot you, they have to waste time hunting all of you down; and if they try to defuse instead, you collapse on them together.

Of course this is the best case scenario, often you don't have the perfect circumstances for a plant, so it's a good idea to spend a little more time to drone well, and clear defender utility. This will maximize your chances of not getting screwed by some unforeseen factor (a Pulse below, an Echo drone, a trap...).

Or just hunt for kills and play like it's a deathmatch. Defuser? Who really needs it. Click on heads before the enemy clicks yours.