“Controlling thought” is a misnomer. Meditation is more a practice of managing attention.
In the beginning, as thoughts swirl, the practice is to remove attention from the thought. Allow your attention to simply rest as much as possible, even though thoughts are clamoring for your attention. Sometimes, the attention will get carried away by the thought. This is a habit we have all developed. Simply notice when this has happened, and allow the attention to rest again.
It can help to give the attention an anchor by placing attention on the inflow and outflow of breathing, or by directing it towards a feeling of love and acceptance of the thought. Both of these are anchors which help wean our attention from thought.
When attention gets carried away, the habit of self-judgment may kick in. We have all been trained to achieve and succeed in the eyes of society, and that generally means we should not make “mistakes.” But getting carried away by thoughts is not really a mistake; it’s how we were trained. If we want a different result, it’s simply a matter of untraining and retraining. If a feeling of guilt or self-judgment kicks in, recognize that this is something handed down to you by others who likely judged themselves. It’s a hand-me-down. When this is recognized, the self-judgment begins to fall away. It wasn’t your judgment to begin with.
The ultimate goal of removing attention from the thoughts is to free up our attention and allow the mind to settle, opening the door to greater possibilities.
(Also see The Three Stages of Meditation)