"To seize the initiative" refers to taking control or making the first move in a situation. It means being proactive and taking charge in order to gain an advantage or control over a particular situation or project. Full definition
From the beginning he laid daily plans to seize the initiative from his opponent. (si.com)
In the absence of federal legislation, some states have already seized the initiative and could set the tone for the rest of the nation. (scientificamerican.com)
In a deeper recession, marketers can benefit by cleaning up their product lines and so should seize the initiative early rather than waiting to be forced into making changes. (hbr.org)