I've got 16mm EKHD fittings, you can barely pull them out with force so you don't need glue if you use something like that... From my bending (which I did entirely by hand with no guides) my tips are:
1. Make sure your bending insert fits nice and snug. If it is not, don't 'try and make do' it will be a futile waste of time... If it's way to tight and won't even fit sand it a little at a time and clean off dust thoroughly.
2. Lubricate it, olive oil works brilliantly - high boiling point etc. Don't use water, this will make life much easier...
3. Don't over heat it, it actually creates much smoother bends when it is not a floppy mess with a little resistance as you bend.
4. Use PETG tubing, that stuff is crazy tough and will not shatter (JayzTwoCents has a video hitting it with a hammer it won't break).
5. It will take you some time to get going, do not rush. Do not get annoyed the bend took you ages. Do step back and smile at that first perfect bend then crack on and recreate it.
6. Cool using an air fan, I held mine over the fan whilst I bent it as I found it very easy to fine tune my bend as it firmed.
7. Lubricate the fitting O-Ring with a little distilled water/fluid when fitting (literally moisten your finger and run it over) as it will be easier to fit and avoids damaging the seal.
8. Order some spare tubing, not only will you make a few mistakes as you've probably discovered stock is a bit hit and miss on hardline so having £10's worth of spares in your draw is not a bad idea.
Good luck!