Answer: That depends. As a general rule, except in questions, it isn't wrong to follow the common English word order of subject, verb, object (if there is an object, also noting that object pronouns can come before verbs or be attached to them). But while English allows variation primarily for questions and poetic effect, in Spanish ordinary statements can start with the subject, the verb or the object. In fact, starting statments with the verb is very common. All the following sentence constructions are possible as a translation of "Diana wrote this novel":
- Diana escribió esta novela. (Subject comes first.)
- Escribió Diana esta novela. (Verb comes first.)
- Esta novela la escribió Diana. (Object comes first. In this construction, an object pronoun is often added to help avoid ambiguity.)
So do all those sentences mean the same thing? Yes and no. The difference is subtle (in fact, sometimes there is no substantive difference), but the choice of wording can be a matter of emphasis rather than something that might come across in a translation. In spoken English, such differences are often a matter of intonation (which also occurs in Spanish); in written English we sometimes use italics to indicate emphasis.
The first sentence, for example, the emphasis is on Diana: Diana wrote this novel. Perhaps the speaker is expressing surprise or pride about Diana's accomplishment. In the second sentence the emphasis is on the writing: Diana wrote this novel. (Perhaps a better example might be something like this: No pueden escribir los alumnos de su clase. The students in his class can't write.) In the final example, the emphasis is on what Diana wrote: Diana wrote this novel.
In Spanish questions, the subject almost always comes after the verb. ¿Escribió Diana esta novela? ¿Qué escribió Diana? Did Diana write this novel? What did Diana write? Although it is possible in informal speech to phrase a question like a statement as can be done in English ¿Diana escribió esta novela? Diana wrote this novel? this is seldom done in writing.
And keep in mind, of course, that in Spanish the subject can be omitted if it is understood in the context. Diana es mi hija. Escribió esta novela. Diana is my daughter. She (omitted in Spanish) wrote this novel.