Consider a beginners' course in German. Working with an experienced teacher or tutor and having the opportunity to learn with and from other students will greatly enhance your conversational skills.
Favor textbooks that have accompanying audio materials. Hearing native speakers interact is one of the fastest ways to improve your skill level. Whether it's your teacher or an audio recording, imitate and repeat clearly to practice your pronunciation as well as your confidence level.
Focus on the vocabulary you need to use most commonly. For instance, if you're in a fashion-related field, you'll probably want to know that a slightly flared skirt is "ein leicht ausgestellter Rock" in German (odge.info). Personalize your learning in this way to get the most out of your experience.
Make time to study every day. German has many grammatical features, such as its system of noun and adjective cases as well as its unique syntax, which require regular review and practice. Aim for at least an hour's practice every day.
Concentrate on paradigms, the broad rules that apply to most words, and the most common exceptions. Since conversation, as opposed to written communication, is your goal, focus on being understood as opposed to technical perfection.
Speak frequently with a conversation partner or with several. As your skills improve, challenge yourself to speak only German as much as possible, as immersion environments force you to be creative on the spot. Use the words you already know to express yourself, picking up extra hints from your partners.
Watch German television and movies. People speak more naturally in these media, except for the news, than in grammar exercises and novels. Since your goal is conversation, imitate the forms and phrases you hear here. For instance, if a particular usage requires the genitive but is replaced by a dative expression by speakers you observe ("trotz dem" vs. "trotz des"), prefer their usage over what is, strictly speaking, grammatically correct.