I would plan activities in various ways such as an informal discussion with the teacher about what weekly and daily activities will be taking place.
You are aware in advance of what you are required to do. There are clear roles and responsibilities for you working together with the teacher to support the pupils. Planning activities is also based on pupils individual needs, abilities and interests hence the importance of accurate pupil observations and assessments also the continuous cycle of identifying leaning needs, preparing, organising and implementing learning activities. The work you are covering fits in with the activities and topics which have been planned for the term. The objectives of the learning activity and the type and level of support the pupils may need.
The teacher may put some time aside to discuss each week’s activities with the teaching assistant. This would allow for any suggestions to be made on how to improve or change things. Teaching assistants should have a clear understanding of the learning objective for each activity and know what they should be doing to help the children achieve this. There could be some children with special needs in the class and so will have different aims to the other children and may also require more support.
The teaching assistant can plan setting up the room with the correct resources before the lesson takes place and laying out the tables and chairs etc, also support may be needed for some pupils, this should have been discussed before the lesson. The teaching assistant could work with one specific table or group of children or just go around the classroom and be available if any of the children ask for help and to identify future learning