[Pollster1]

The real strategy is to get delegates selected that are loyal to you. Courting them afterwards is not very effective.

That is not always possible. The state party chooses the delegates in some states. It would be nice if a few of the chosen delegates actually liked Trump. Jeb/Carson/Rubio chose a few of them who are now unbound. It would be nice if a few of those unbound delegates actually liked Trump now. Choosing your own delegates is better, but it is not always an option.

[DrewsDad]

In most states, the delegates to their convention vote for the national delegates or at least vote to approve (or reject) the report from a nominations committee with a slate of delegates. If a campaign is organized and has their supporters there, then they can influence the selection.

For those states that limit the grassroots influence, you move to change the rules on how the delegates are selected through the rules committee.