Am new to photoshop (have been using Lightroom) and have been working my way through various tutorials but am not sure of the correct way to save a photo. Sometimes I can have 10 different layers to one photo before finishing them off in another programme. Should I be merging all visible layers or flattening them before saving them as. a JPEG/Tiff/PSD?
Would be really grateful for advice and help.
My recommendation is to keep the original file with the layers and save a copy of the file if you want a flattened version. Saving as a jpeg will automatically flatten the layers since jpeg doesn't support layers.
A way to have your cake and eat it too:
Highlight all of the layers (on a copy -- be sure to save the original) and then Ctrl-Alt-Shift-E will keep all of the original layers and create a new flattened layer above the other layers in the layers panel.
Always save a master copy and keep all the layers etc. Save this as a PSD (or TIFF).
Then if you need a jpeg copy for example to send somewhere or post on the web use Export - Save for Web to export a copy of the file sized according to need.
One final bit of advice - if you are building up a large document involving lots of work and layers then save incremental masters as you go e.g. filename_001.psd, filename_002.psd ....etc . These can get you out of a lot of trouble if you have a crash or realise you have made a big mistake along the way. You can always delete them and keep only the main master once you have finished.