What are the do's and don'ts for an engagement party?

Short answer

Do keep it relaxed, tell guests it is an engagement party, and thank them for coming. Don't make it a mini wedding, don't expect gifts, and don't invite people you won't invite to the wedding, unless you are clear it is a separate celebration.

Do send clear invitations that say 'engagement party' so guests know what to expect. Do choose a date soon after the engagement, while the excitement is fresh. Do keep the guest list small, often close family and friends. Do introduce people who do not know each other, especially if families are meeting for the first time. Do have a short toast to the couple, but keep speeches brief. Do thank your hosts, whether that is you, your parents, or someone else.

Don't treat it as a rehearsal for the wedding. Avoid the full wedding structure, like a sit-down dinner with multiple courses, a DJ, or a formal dress code. Don't expect gifts. Some guests may bring a card or a small present, but it is not required. Don't feel you must invite everyone who will come to the wedding. It is fine to have a smaller group. However, be careful about inviting people to the engagement party who are not invited to the wedding, as this can cause hurt feelings. If you do, be clear that the engagement party is a separate, smaller celebration.

Don't announce the wedding date or venue unless you have confirmed them. Don't let the party become stressful. The point is to enjoy your engagement. Keep it simple, and you will have a lovely time.