Interrogatories are written questions served on a party, answered in writing and under oath. Most courts limit the number, counting discrete subparts separately, which is why the drafting is compressed.
What they are good for. Identifying people, entities, accounts and documents; pinning down dates and amounts; forcing a party to state its contentions and the facts supporting them. Contention interrogatories served late in discovery are among the most useful tools available, because the answer frames what must be met at trial.
What they are poor at. Anything narrative. The answers are drafted by counsel, and a well-drafted answer to a broad question tells you very little. Depositions are where the story is tested.
Objections must be stated with specificity, and boilerplate strings of objections followed by an answer subject to them are increasingly sanctioned. State the objection, state whether responsive material is being withheld on that basis, and answer the rest.
Business records option. Where the answer can be derived from records and the burden is substantially the same for either party, a responding party may specify the records instead of compiling the answer. The specification must be precise enough for the requesting party to locate them.
Supplementation is a continuing duty. An answer accurate when made and false by trial is a serious problem, and the fix is a diary date, not memory.