If you are traveling to the country with entry visa regime then you need to apply for entry visa in advance.
Coming from Visacenter experience there may be a list of reasons why your visa application may be delayed in its processing or rejected completely.
Reasons for your visa application to be delayed:
1. Visa application form is incomplete, i.e. while completing it you have omitted one or several items.
2. Visa application is not signed and/or not dated.
3. Visa application form is not in the required form. Many countries now require that visa application form be first filled-out on-line and then printed out. This apply, for example for visa application forms for Russia, Brazil, India. Some of them, like China, requires that visa application forms must be filled out on your computer and then printed, but not filled out by hand.
4. Passport is not signed by the owner. There is a special place on page 3, usually, where the holder of this document must put the signature.
5. Passport is damaged. It applies to obvious damage, like torn pages, cover(s). Unauthorized, non-official markings on the page (like scribbles made by your child or notes by yourself). Or less obvious, like when you wash your passport. It may seem OK to you, but not to the visa officer at the consulate.
6. Photo is not up to the requirements. Photo-booth are absolute no-no these days and self-made photos are not acceptable in many cases. You have to take your photo at any Visacenter office or at the professional outlet, like Wal-Mart, Costco, etc.
7. Additionally required documents are not presented, presented not in full or do not meet the standards. Each country has a different list of the documents that must be submitted along the core ones (passport, photo and visa application form). In some cases it is an invitation from the person or organization from that country, or /and bank statement, printed out itinerary, International Certificate of Vaccination for Yellow Fever, etc.
8. Payment of consular visa fee is in-correct: it may be incorrect amount or form of payment. Most consulates are accepting only money-orders, so sending them cash or personal cheque is incorrect form of payment.
9. Incorrect mailing address. In many cases the consular divisions of the embassies are located at addresses different from the address of the embassy premises. If you send your visa application to the embassy it will be definitely delayed in processing.
10. No return pre-paid envelope/waybill enclosed to return your passport with visa or enclosing the envelope of the service that the consulate is not using. Some consulates for example are using only certain courier companies and if you attach pre-paid waybill from different company they do not send it back to to you.
11. Political and/or consulate relations between two countries. Sometimes when the relations between the countries are getting worse, this may negatively reflect on visa issuance processing.
Reasons for your application to be rejected:
1. You are black-listed by the country where your are going to.
2. You have provided false, in-complete information or failed to meet additional requirements or failed to attend visa interview at the consulate.