Good news: Spanish is highly phonetic — once you know the rules, you can pronounce almost any written word.
The five pure vowels
The foundation of a good Spanish accent. Each vowel is one clean, consistent sound — always — unlike English's drifting vowels. Get the five right and you're most of the way there.
The consonants that trip people up
A handful to watch: b and v (the same sound), the soft d, g and j, the silent h, ñ, and ll/y. None is hard once you know what it does.
Stress and the written accent
Simple rules govern where the stress falls, and the accent mark tells you when a word breaks them. Learning this fixes a surprising number of mispronunciations at once.
Linking
In connected speech, words run together. Knowing this helps both your own accent and — just as much — your ability to follow native speakers.