Make sure you allow enough time in your project plan for designs and drawings to be approved, internally as well as by the client.
It is common to need 1-2 weeks for each step of FDR (Final Design Review), IDC (Interdisciplinary Check), Verification, IFC (Issue For Construction) etc reviews and approvals, especially if more than one person must approve these.
It is important to keep track of the approval status of these and follow up on people to review and sign them. I often find that although people get notified, they overlook signing the reviews or it sits on a desk waiting and gets buried.
If all the approvers are collocated, it is often worth having someone walk the documents around personally to each person for their approval, this can dramatically reduce the time taken and stop the documents being buried under other work or being forgotten about.