You can first discuss the budget with htb... Brainstorm where to go... What kind of vacation you both enjoy? (beach, exotic places, watersports, trekking, nature, climbing, shopping, farmstay, etc)
Then you can research the shortlisted destinations about when is the best time to visit, weather, etc.
Go by tour or f&e...
Ask colleagues, friends and family for their experiences and opinion.
Then, select suitable dates to go...dont have to be immediately aftr the wedding. Just choose a convenient and comfortable date.
Oh..and remember to buy insurance.
Hope this helps!