These are some notes that may be helpful to Schengen applicants. There is no absolute formula guaranteeing success; some applicants are successful submitting less and others require more. It's down to each applicant to use their best judgement and select the highest quality evidence they can get.
Is a visa necessary?
You do not need to apply for a Schengen visa if you have a category "D" visa from any of the member states. Category "D" visas include...
- Student Visas
- Work Permits
- Settlement Visas
- Residence Permits
If you already hold one of these, you can use it to travel to any of the other Schengen states. Otherwise keep reading...
If you are using the internet to research your application, remember that the 'official' documentation is found within the 'europa.eu' address. It means the URL should end with 'europa.eu' URLS that end with '.com' or '.co.uk' are commercial enterprises and may not contain current or accurate information.
There is no comprehensive 'official' guidance for applicants to refer to, it is down to the individual countries to publish guidance. France, for example, has a 'how to' page. Germany has a Guidelines Document. Since the application form is uniform for all Schengen members, much of the information found in these two resources can be used for any country.
Photograph, passport, application form, and biometric enrolment. These are all documented at the various member sites and not worth going into here.
This usually takes the form of a statement. It should include an explanation of why you want the visa, and what you plan to do during your stay. The premise should be coherent and make sense in the context of your age, life-style, profession, social standing and so on. A failed premise can be grounds for refusal so it's worthwhile taking the time to be sure your premise is complete and tenable. Note: first time travellers and young travellers should be especially diligent to be sure that their premise is well conceived.
Note: your premise will govern whether or not you need a single entry or multiple entry visa. It will also determine which consulate you should apply to.
If your visit includes multiple places, then this is a list of where you plan to be on each day of your visit. It should dovetail with your 'proof of accommodation' evidence (see below). Note that the itinerary can be supported by showing that you have the minimum daily subsistence level for each day and country you plan to visit.
This is a list of items you are including as evidence (see below). Sometimes it may be helpful to annotate the various items to explain why you think they should look at it.
Returnability: If you are not a permanent resident in the country at which you are submitting your application, you will need to include something that establishes that you can lawfully return. You can use a residence permit, a long-term visa, or similar document to show that you can exit the Schengen zone to your residence without any problems.
Proof of family ties: This can be helpful in establishing your willingness to return home. There is no explicit standard governing what to submit or what will be deemed acceptable. Consider including one or more of these: a marriage certificate, children's birth certificates, tax returns that list all family members, a photo of a family event. If you do not have family ties, consider other evidence such as church and social affiliations or any other evidence that establishes a public profile. If the children are not accompanying the applicant, then consider explaining how they will be cared for during the trip.
Proof of employment: This should be an employment contract which is supported by salary slips. If you are unemployed and relying upon the support of a sponsor, then the sponsor's employment contract and salary slips should be submitted instead. If you are self-employed, you can consider submitting your formation document, VAT returns, corporate web identity, and most importantly your corporate tax returns. If you have not been submitting tax returns, consider filing retrospective returns to help show that your funds have been lawfully obtained. Tax delinquency can be used as grounds for refusal.
Travel medical insurance: The required travel insurance is clearly shown on the Schengen site where you are applying. This is a statutory requirement without discretionary latitude.
Proof of accommodation: Confirmed hotel bookings are the highest quality and secondarily an invitation letter from a private host. The invitation letter should note the relationship between the applicant and host and the dates of accommodation. The host should explain their capacity to offer accommodation, so if the host does not own the property, then consider including evidence from the host's landlord giving permission for you to stay. If permission is given explicitly in the host's tenancy agreement, then include the tenancy agreement with the relevant text highlighted. Couch surfers should follow the same pattern as confirmed hotel bookings. If a business is offering to pay for your hotel, you can include the bookings they make on your behalf (along with an explanation of why they are paying for you). Proof of accommodation is a statutory requirement without discretionary latitude.
Letter of liability: if a third party host is providing subsistence or accommodation for your visit, they may need to procure an official document declaring their personal liability. These requirements vary on a country-by-country basis. For some Shengen countries, the letter of liability is a statutory requirement without discretionary latitude.
Movement of minors: If minors are to cross international borders, you should submit evidence of consent from the parents listed on the child's birth certificate. If this cannot be done because a parent is separated/divorced, then consider the child's custody order or similar document so that the relevant Hague Convention is complied with. A perceived (or suspected) violation of the Hague Convention is grounds for refusal.
Tickets: There are two scenarios 1 Return. the applicant will visit the zone and return to his home country; 2 Transit. the applicant will visit the zone and then travel to some other place (e.g., an around the world trip). Return/Transit flight reservations (or train return/transit reservations, etc) are required, but it is emphatically recommended not to purchase tickets outright in advance of the application. If in doubt, it's fine to include a statement that you will make a personal appearance with paid tickets when the visa is issued and you are collecting your passport. The applicant can present either evidence showing a return to his home country or showing onward travel (transit). When submitting transit evidence they will check to assure that the applicant has a visa for the next location (or is admissible without a visa). Round/Transit trip evidence is a statutory requirement without discretionary latitude.
Proof of subsistence: This usually takes the form of bank statements for the most recent three months. The bank statements should be originals. Again, note the minimum subsistence requirements. If you do not have a bank account or you are relying upon a family member or other type of third party, then you should provide an explanation and provide their most recent bank statements instead.
Movement of funds: Each deposit into the bank account should be traceable to a salary slip or some other evidence that the funds have been lawfully acquired. If your parents deposited money into your account, then you will need to include their salary slips and bank statements as well. If you are self-employed and living out of your pocket, consider submitting tax returns along with sales receipts. Failure to establish the provenance of funds can be grounds for refusal.
Relationships: If you are planning to stay with a boyfriend or girlfriend, it makes sense to be transparent about it. Trying to hide it may give the appearance that your itinerary is not genuine and this may cause credibility problems. If your host is a family member, but not in the ascendant or descendent line, it makes sense to explain why they are sponsoring you at this particular time. If you have been invited on a professional basis to attend meetings or negotiations, their letter should explain your relationship to them and include an agenda.
Notes: Not all of these things are applicable for every applicant. You will need to rely upon your judgement to determine which things are helpful for you. Your judgement will also be helpful in determining the right level of evidence; throwing tons and tons of stuff at them may backfire because they will not have the time to look at everything and your application may be refused as 'incoherent'.
The controlling reference for this answer is The Schengen Visa Code.