I was asking similar question several days ago. The answer I got is that you should feel the skin under your chin tighten up when getting the tongue up on the roof - that means you engaged the posterior third of the tongue. Think of bringing your hyoid bone up, I guess.

ok should i be pushing the hard palate with my tongue or suck up onto it or just hold my tongue against it?

You need to close your teeth gently together, lips together, rest the tip of the tongue on 'the spot' and then push the rest into the roof of your mouth, but don't try to force it up there or the teeth will part and the muscles below your chin will expand (I look like a frog like this). Only use enough force as to not make your teeth/jaws come apart. Try to flatten the middle of your tongue against the roof of the mouth and get the back up as well (this last bit is important). Do not touch the front teeth with the tongue. You should be feeling the soft palate with the back of the tongue a little. 

Full guide here: /community/guide-to-proper-tongue-posture-mewing/

It took me around 3 weeks to find a comfortable spot like this, there can be many reasons as to why.

Explanation here: /community/common-tongue-posture-mewing-problems-and-solutions/

Learn the mona lisa swallow technique from Dr. Mew (on youtube)

Getting below 15% body-fat also helps with jawline definition and hollow cheeks a lot. Look up intermittent fasting as it increases human growth hormone which is useful to you as you try to move bone here. Its healthy otherwise as well. IF you also train or do some sports, look into HIIT (High Intensity Interval training) it increases human growth hormone as well.

I recommend taping your mouth shut during the night with tape that does not leave a mark and stays on. Do this until you get used to closing it. I use 3M paper tape.

Dont forget to do chin-tucks and to correct your posture, also for motivation check out the success stories. Some ppl even as old as 50 have made AMAZING bone structure gains, especially mandible positioning and definition.

For chewing I recommend getting mastic gum / tears. Its antibacterial so u can freeze it and reuse (cus its expensive) and it looks like resin. When you chew it, it breaks and forms a yellow-white really hard gum (so hard you cant even mold it with your tongue). Careful if you don't chew hard enough or fast enough it solidifies into resin again. Every time you re-chew it at first it will break apart and then reform as gum... try not to swallow the bits XD.. also warning it may break loose teeth lol or shitty filings... its really chewy and tough as nails. Chewing it might make your vision blurry at first. Brush teeth before chewing if you plan to re-chew the same gum. I chew for 30 min to 1 hour on each side, that's 1 to 2 hours daily. <== not recommended if you are female, it will hypertrophy the chewing muscles, make the bones togher and make you look manly. Failing to maintain proper neck and back posture during chewing can cause TMJ.

Thank you this is very comprehensive I appreciate the response since im sure this question and every variate of it have been asked numerous times.

This is exactly what happens to me too? Whenever I try to mew, my submental area gets push downwards. Is it supposed to go updwards?

@greekgodbrody

Did you find out ?