Define what a message is for
'Message me any time' can mean several things. A trainer may mean that you can send a scheduling question whenever convenient, not that they monitor the phone continuously. Ask which channel to use, what questions it covers and when to expect a reply. Put the arrangement alongside the session schedule so it is easy to find.
Separate booking administration from coaching feedback. A change of appointment may go through a reception team, while a question about something taught in a session may go to the trainer. Sending everything through a social media comment can expose personal information and make an important message easy to miss.
Ask whether reviewing notes or videos between appointments is included in the price. If it is an additional service, find out how it is charged before sending a large set of recordings. More contact is not automatically better support; a clear, manageable exchange may be more useful than an open conversation that neither person can follow.
Write a question that can be answered
Give enough context to identify the issue. Mention the session or exercise you mean and say what part of the explanation is unclear. 'Which adjustment did we use on the seat?' is easier to answer than a photograph with no question attached. Avoid sending sensitive details through a channel the provider has not agreed to use.
Some questions need to wait for an in-person demonstration or a different professional. A delayed reply is not a safe basis for continuing something you are unsure about. Between-session messaging is also not an emergency service; do not use an expected coaching response as a substitute for urgent help.
Review the arrangement if it stops working. Perhaps one consolidated weekly message suits both people better than frequent fragments, or a short booked call is needed. Confirm any change in scope or cost. A communication agreement should make it clear when support is available and what happens when it is not.