You do not create a Lookup Dialog. It appears automatically on every lookup field. What you configure is what it shows and which records it offers. The two highest-value settings are the Search Results search layout (columns) and lookup filters (scope), both per object in Setup.
- Open the object's Search Layouts
In Setup, go to Object Manager and select the object whose lookup you want to improve, for example Contact. Click Search Layouts, then find the Search Results layout used by Lightning Experience. In Salesforce Classic, edit the Lookup Dialogs layout instead.
- Add meaningful result columns
Edit the Search Results layout and move fields such as Account Name, Email, and Title from Available to Selected. These become the secondary details under each suggestion, so users can tell similar records apart. Save the layout.
- Add a lookup filter to the field
Go to the lookup field itself (Fields and Relationships, then the field, then Edit). Define a Lookup Filter, for example Account Type equals Customer, to limit which records the dialog offers. Decide whether the filter is Required or Optional.
- Make it dependent where it helps
For a dependent lookup, set the filter to reference a field on the current record, such as limiting a Case Contact to the Case's Account. This narrows the dialog based on earlier choices on the same page.
- Test as a restricted user
Log in as, or impersonate, a user on a limited profile and open the lookup. Confirm the right records appear and the columns read well. Sharing and filters can hide records that an admin sees, so verify the real user experience.
Per-object layout in Object Manager that sets which fields show in Lightning lookup suggestions and global search. Classic uses a separate Lookup Dialogs layout.
Admin-defined criteria on the field that restrict which records the dialog offers. Can be Required (blocks an invalid save) or Optional (user can toggle it off).
A lookup filter that references a field on the current record, so the dialog's choices depend on a value already entered on the same page.
Up to six Lookup Filter Fields an admin specifies so users can filter the Classic enhanced lookup popup at search time. Needs the Customize Application permission.
- Lightning typeahead matches the Name field only. Users searching by email or phone must click Show more results to run an advanced search across all searchable fields.
- A newly created record may not appear in recent items until the user starts a new session, because records enter the recent list when created or edited.
- In Lightning Experience there is no separate Lightning lookup layout; the Search Results layout drives both lookup suggestions and global search, so changes affect both.
- The dialog enforces sharing. A record an admin can see may be invisible to a restricted user, so always test lookups under a limited profile.