You obviously need a set of rubrics depending on the speaking task (narration, give opinion and justification for or against, role play, describing and contrasting pictures) you will be giving the students. Each task will prompt students to exhibit certain language skills than another may not. Why not take a look at the teacher handbook for the KET, PET and FCE certificates, for example.
Well! I think that the assessment method here and the criteria depend largely on your goals and focus (accuracy vs. fluency). Generally, rubrics are used in this case to assess oral performance (e.g. from 1= INADEQUATE to 5=EXCELLENT). The main criteria that are commonly used might be: appropriacy, fluency, style, and communication. Good luck
My MA thesis is about assessing the speaking skill using an alternative assessment tool, which is rubric. It's entitled "The Impact Of Using Scoring Rubric In Peer Assessment On Promoting Iraqi EFL Learners' Speaking Skill In The University Level".
I've designed the rubric, tested the students' speaking skill before applying the rubric (as a teaching method- as well as an assessment tool) then made a post test at the end of the course of the study (experiment). The results were really interesting, the majority of the students liked the use of the rubric, and it really helped promoting their performance as well as behavior.
You may check the thesis, it's available for download .
I agree with Dr. Nashwa Nashaat Sobhy! Teachers can develop or adopt rubrics depending on activities which can help assess oral proficiency of the students. Please refer to the following article as well:
Halleck, G. B. (1995). Assessing oral proficiency: A comparison of holistic and objective measures. The Modern Language Journal, 79(2), 223-234.
Cambridge University has designed a website which is entitled" speakandimprove". It is a robot that evaluates the speaker's performance by answering some questions. The speaker can gradually move from level to level based on his performance.