Founder vesting/sweat equity: What happens if a founder leaves after three months? Make sure no one leaves with 30% without having put in the 'sweat'.
Board composition and decision rights: Who is on the board and what types of decisions can be made with what majorities (e.g., who can fire the CEO)?
Purchase options: In certain "trigger events", such as a founder leaving as a "bad leaver", the other shareholders have the right to buy the shares at a defined value.
Righ of First Refusal (ROFR): Before a shareholder can sell their shares to another party, they must offer the shares to the other shareholders. This is the controlling the shareholder structure.
Drag Along: A prospective buyer will always want to purchase 100% of the shares, not 99.9%. With the drag-along, a certain majority of shareholders can "drag along", i.e. force, the minority shareholders to sell theirshares. If you have a large number of minority shareholders, it is important to consider the enforcement mechanism.
Tag Along: If the majority of shareholders sell their shares to a new buyer without triggering the Drag Along, the minority shareholders may not want to be minority shareholders with the new buyer. To protect the minority, the minority has the right to "tag along", i.e., sell their shares to the new buyer.
IP assignment: If shareholders are working for the company (e.g. as founders), it ensures that the IPcreated is assigned to the company.
Non-compete/non-solicitation: Since shareholders have extensive insight into the company, having a non-compete and non-solicitation clause protects the company's business, know-how and clients.
Confidentiality: It is important to keep the agreement and any information exchanged confidential. However, always have a carve-out that allows you to share the agreement for a financing round.
Amendments: A 100% approval requirement gives minority investors the power to block a subsequent financing round. In general, you can't impose new obligations on old shareholders; the main exception is the introduction of a liquidation preference in subsequent financing rounds.