How to skip play in ansible-playbook?
Although the comments have highlighted the fact that this playbook is fine, as long as it is designed to do what it needs to do:


  The reason behind this is that, the first play will create ansible user with sudo access. Here, I have used root user to run the play. Then I have to run another play as ansible user.


In the first play, you have only one role: role1. If in role1 you have a task that creates the ansible user, then you can use that user to connect the next time. This is actually something many people do, including myself, to put a known baseline on a service:

- name: Ensure Ansible user is present (RedHat)
  user:
   name: ansible
   comment: "ansible user created by bootstrap playbook"
   generate_ssh_key: yes
   groups: wheel
 tags:
 - bootstrap
 when: ansible_os_family=="RedHat"

- name: Ensure Ansible user is present (Debian)
  user:
   name: ansible
   comment: "ansible user created by bootstrap playbook"
   generate_ssh_key: yes
   groups: sudo
  tags:
  - bootstrap
  when: ansible_os_family=="Debian"

- name: update sudoers to ensure ansible user can sudo
  lineinfile:
    dest: /etc/sudoers
    state: present
    regexp: '^ansible'
    line: 'ansible ALL=(ALL) NOPASSWD: ALL'
  tags:
  - bootstrap


This will ensure that the user is added, and included in the right groups, with sudo rights -- it is just an example of how you could achieve this, there are other strategies of course.


  My question is how to run these play one after another? I first want to run first one then after that second one.


That's exactly how playbooks work.


  If I run the playbook then it will get stuck because it will first run first play and tries to run second play where it gets stuck.


If you do not have a task to configure the user required in the next play, then yes, it will fail (not get stuck). 
The point is that since Ansible is idempotent, you don't have to worry about skipping the play because if the user is properly configured, the first play will simply have no effect.

However, to answer the actual question 


  How do I skip a play in an Ansible playbook ? 


This is done using the conditional execution using when