app/views/admin/posts/_form.html.erb
<%= form_for [:admin, @post] do |f| %>
<div class='form-group'>
<%= f.label :title %>
<%= f.text_field :title, class: 'form-control' %>
</div>
<div class='form-group'>
<%= f.label :body %>
<%= f.text_area :body, class: 'form-control' %>
</div>
<div class='form-group'>
<%= f.collection_check_boxes :tag_ids, Tag.all, :id, :name do |t| %>
<div class='checkbox'>
<%= t.label do %>
<%= t.check_box + t.text %>
<% end %>
</div>
<% end %>
</div>
<div class='form-group'>
<%= f.submit "Save", class: 'btn btn-block btn-success' %>
</div>
<% end %>