Link directly to specific tab. Add ?tab=3 to the URL to jump straight to tab3, for example.

server.R

shinyServer(function(input, output, session) {
  # On startup, read the URL parameter
  queryParams <- parseQueryString(isolate(session$clientData$url_search))
  if ('tab' %in% names(queryParams))
    updateTabsetPanel(session, 'tabset', selected = paste0('tab', queryParams[['tab']]))
})

ui.R

shinyUI(fluidPage(
  tabsetPanel(id = "tabset",
    tabPanel(value = "tab1", "One"),
    tabPanel(value = "tab2", "Two"),
    tabPanel(value = "tab3", "Three")
  )
))