1. Block individual users
You can block individual members to prevent a contact from that person permanently. This can be done through the respective profile (see under options menu) or directly in a conversation in the title bar options menu. If you have blocked a person you will get no more messages from this member. The blocked member can still view your profile.
An overview of all of your blocked profiles can be found under Settings > Blocked members.
2. Exclude certain groups of people
With Lovely it's very simple to get rid of unwanted new contacts. Just switch on Filter > Who may send chat requests > Only matches. Then only people you previously liked can contact you.