Practice saying "almejas" (see third Reference) until you're comfortable with the pronunciation. In Spanish, the letter "j" is pronounced the same way the English "h" is. The word doesn't contain any accents but, when spoken, stress is put on the second of the three syllables.
Remember that all Spanish nouns are either masculine or feminine and singular or plural. Because "almejas" is a feminine noun and plural, it should be preceded by the word "las." So, the correct term is "las almejas." If you're talking about just one clam, the correct term is "la almeja."
Include the word in entire sentences that you might use while on vacation or in conversation with Spanish-speaking friends. For example, you might say, "Anoche comi un plato de almejas." This translates into "Last night, I ate a plate of clams."