How to insert multiple values from form, including multiple checkboxes

there!

I have this HTML:

<form method="POST" action="incluindo1.php">
        <fieldset>
            <legend>Incluir Produto</legend>
            <label for="nome">Nome:</label><br>
            <input type="text" name="nome" class="" placeholder="Digite o nome"><br>
            <label for="email">Email:</label><br>
            <input type="email" name="email" class="" placeholder="Digite o email"><br>
            <label for="categoria">Categoria:</label><br>
            <select name="categoria">
                <option value="selecione">Selecione</option>
                <option value="a">A</option>
                <option value="b">B</option>
                <option value="c">C</option>
                <option value="d">D</option>
            </select><br>
            <label for="preferencias">Preferências musicais:<br>
                <input type="checkbox" name="preferencias[]" value="Clássica">Clássica
                <input type="checkbox" name="preferencias[]" value="Rock">Rock
                <input type="checkbox" name="preferencias[]" value="Pop">Pop
                <input type="checkbox" name="preferencias[]" value="MPB">MPB
                <input type="checkbox" name="preferencias[]" value="Flashouse">Flashouse
            </label><br>
            <textarea name="observacao" class="" placeholder="Digite sua observação"></textarea><br>
            <input type="submit" value="Incluir" name="incluir" id="incluir">
        </fieldset>
    </form>

And I have this PHP:

include "conecta_mysqli.inc.php";

$nome=$_POST["nome"];
$email=$_POST["email"];
$categoria=$_POST["categoria"];
$preferencias=$_POST["preferencias"];
$observacao=$_POST["observacao"];

$inclusao = mysqli_query($conexao, "INSERT INTO pessoas_a VALUES(null,'$nome','$email','$categoria','$preferencias','$observacao')");

And this SQL:

create table pessoas_a(

id int(11) AUTO_INCREMENT, nome varchar(50) not null, email varchar(30) not null, categoria char(1) not null, preferencias text not null, observacao text not null, primary key(id) );

How is the best way to insert those values in MySQL