Familiarize yourself with the Spanish alphabet if you haven't already. The Spanish alphabet contains the same letters as the English alphabet, with four additions: "ch," "ll," "ñ," and "rr." Remember these four letters when spelling.
Watch for the use of accents in Spanish vocabulary. Many Spanish words, such as "zapatería" (shoe store) contain accents that are used to show the speaker which syllable of the word they should place the emphasis on when talking. Accents are extremely important to include in your spelling because some Spanish words are spelled the same with the accent being the only difference between the two words (for example, the word "hacia" means "toward" while the word "hacía" means "he/she did").
Remember that all words in the Spanish language have gender and that gender must be considered when spelling. All Spanish words that are feminine begin with "la" (i.e. "la montaña," or "the mountain"), while all masculine words begin with "el" (i.e. "el coche," or "the car").
Use a Spanish dictionary to aid you in your spelling. Just like you would in English, use the Spanish dictionary as a reference tool to help you if you're not completely certain how to spell a word. It is vital to spell a word correctly or you may end up spelling an entirely different word and thus change the meaning of what you're trying to say.