Here are the steps for string crossings:
1. Start by placing the bow on the desired string with a slight angle towards you (this is called the 'hairline').
2. Apply a small amount of pressure on the bow so that it can grip the string.
3. While keeping the bow in contact with the current string, move it smoothly and swiftly towards the adjacent string.
4. As the bow changes strings, maintain a consistent bow speed and pressure to ensure a seamless transition.
5. Continue playing the note on the new string with the bow.
By practicing this technique, you can change strings smoothly without breaking the sound and produce a legato (smooth and connected) sound. It might take some practice, but with time and effort, you'll master the art of string crossings on the violin.