Ask local advice in your hotel or accommodation for areas to avoid and crimes to watch out for.
Be careful after dark even in central Marseille, as you can become easy prey for muggers.
Don’t go down quiet back streets where you are more vulnerable especially at night.
Don’t leave valuables unattended on the beach or in your car. Be careful around the train station after dark and stick to wide well lit streets, preferably those with CCTV.
Single women can be seen as easy targets and may receive unwanted attention from groups of men. It is best not to engage with these people and dressing modestly can help reduce their unwanted attention.
Try not to look like an obvious tourist and keep your valuables hidden or in your hotel.