1. Dress accordingly to the brand you are applying to.
It might take time to research the brand and to adjust your wardrobe with the company's dress code but it will pay off much faster then you think.
Even majority of the brands provide a uniform, they want to see person who's style represents them as closer as possible. If you are applying for a vacancy in one of the fashion giants like Chanel or Valentino, make sure to choose classic look, you can add an accent but you should look like you do belong there. Or if you have chosen more contemporary brand like Givenchy or even Rick Owens, make sure to dress up in a certain way, and it will add some extra points to your success.
Few essential things which are obvious to almost everyone but some people still make mistakes in this field.
1.1 Always take a shower before you start your journey.
1.2 You can use some perfume but do not over dose it.
1.3 Never enter the store wearing sunglasses.
2. Always have a copy of your CV with you.
A cover letter is unnecessary as it will bring more generic feel to your application. Make sure you staple your CV if it contain more then two pages, believe these small details matter.
3. Be kind!!!
I personally will put it to the first place but not that many people make this mistake so it comes on the third place by importance.
If you have decided that only speaking with the manager gets you the job you are wrong. The team members are always aware of the vacancies in the store and they always can comment about you in a positive and uplifting manner or they have a power to put your CV strait to the bin if you are not nice to them.
In my practise so many people were insisting seeing the manager without explaining the reason to the team members, that the only one comment they will give to the store manager that the applicant if rude, not a team member and a time waster etc. Team on the floor knows when it is good time to just take a CV or when the manager is available for the meeting. Be nice, ask about seeing the manager regarding potential vacancies, make a nice comment how great is the store and how nice it should be working here. Then if you are refused with face to face meeting with the manager, just pass your CV to the staff and you can trust me they will make sure your CV reaches the right hands and you will be talked up.
4. Timing is an important thing.
Usually all luxury stores are busier in the afternoon then in the morning or in the evening. Also Thursday to Saturday considered to be pick days for the boutiques or department stores. So, if you choose to bring your CV to the stores before noon in the beginning of the week you will have higher chances to get to speak with the manager or copy of your CV will be taken seriously by the team. But if you bring your CV during the pick time, and will insist on certain things you will strait away be considered not a very good team player who will put his/her interests above the team.