When creating information in Salesforce, there are 'required' pieces of information that must be included in the form. The table below gives you a list of required fields for some common objects in a standard Salesforce implementation:
Account: Name
Contact: Last Name
Lead: Last Name, Company
Campaign: Name
CampaignMember: (i.e. Adding a Contact to a Campaign): Contact ID, Event ID, Status
Event: Subject, Date, Time, Duration (usually defaults)
Task: Subject, Priority, Status
Opportunity: Name, Close Date, Stage
Case: Status (usually defaults to New), Origin
Solution: Solution Title
Product: Product Name
In terms of some common AppExchange applications, here is the required information for a few popular installed Salesforce Lab Apps:
Class Enrollment:
Class: Class Name
Enrollment: Class ID, Contact ID
Project/Issue Management:
Project: Project Number
Issue: Project ID
Recruiting Manager:
Candidate: Candidate Name:
Applicants: Applicant Name
I hope you find this useful. Don't forget, this includes the information you MUST include, you are likely to want to include much more than this...