なら

1. 1If it is the case that …; states a condition or assumption and what follows from it.Ex. 1
2. 2If you are going to (do) …; introduces advice, a suggestion, or a judgment about an intended action.Ex. 2
3. 3As for …; after a noun, takes up a topic someone has raised.

Neutral and common in speech and writing, especially for advice and suggestions that respond to what someone says or intends. Unlike たら or ば, the main clause may describe something done before the condition is realized (日本に行くなら、カメラを買う: buy the camera before going). Noun + なら is also used to pick up a topic just mentioned.

• たらN4「たら」attaches to the た-form and emphasizes doing the second action after the first is realized; it can also express discovering something unexpected after doing the first action. With 「なら」, the second action can occur before the first. For simple hypotheticals like 「雨なら」 and 「雨だったら」, the two are often interchangeable.
• ばN4「ば」 focuses on the condition itself, can express general rules, and forms patterns like 「〜ばいい」 and 「〜ばよかった」; verbs must change form (書けば). When the first clause is an action verb, the second clause generally avoids commands or volitional expressions, whereas 「なら」 often introduces suggestions.
• とN5Only the conditional sense of 「と」 is close to 「なら」. 「と」 indicates that once the first clause holds, the second follows automatically, mostly for rules and habits, and the second clause generally does not take volitional or request expressions; 「なら」 picks up a topic to make a judgment or suggestion, so the two are generally not interchangeable.
• としたら / とすればN3「としたら／とすれば」 emphasizes making a tentative assumption and often pairs with 「もし」 or 「仮に」; nouns and な-adjectives need 「だ」 (「雨だとしたら」). For the hypothetical supposition in sense 1, it is interchangeable with 「なら」; when giving advice based on the other person's plans, 「なら」 is generally used.
• 次第だ / 次第でN2「なら」 sets a specific situation as a premise and then makes a judgment or suggestion; 「次第だ／次第で」 says the outcome changes depending on the first item and depends entirely on it, attaching only to nouns or 「か／かどうか」 clauses. Compare 「雨なら中止」 with 「天気次第で中止」.

たら, ば and と present the condition, whether hypothetical or real, as coming first with the result following from it (と especially for natural or habitual outcomes). なら instead takes up an assumption or something just said, and its main clause can even come before the condition in time. としたら / とすれば stress a purely hypothetical 'supposing that', while Noun + 次第だ / 次第で means 'depends on / depending on' (あなた次第だ), not 'if'.