Sathipathanna mindfulness and Jhana how to do them correctly
The way to develop Satipattana and Jhana is described below:

When, bhikshu, this samadhi has been cultivated, well cultivated by you, then you should train yourself thus:
“I will dwell exertive, clearly aware, mindful,
observing [contemplating] &lt; body | feeling | mind | dhamma &gt; the in the &lt; body | feeling | mind | dhamma &gt;,
removing covetousness and displeasure [discontent] in regard to the world.”
Thus, bhikshu, you should train yourself.
When, bhikshu, this samadhi has been cultivated, well cultivated by you, then, you, bhikshu,
THE 1ST DHYANA:
should cultivate this samadhi with initial application, with sustained application;
should cultivate this samadhi without initial application, with only sustained application;
THE 2ND DHYANA:
should cultivate this samadhi without initial application, without sustained application;
should cultivate this samadhi with zest;
THE 3RD DHYANA:
should cultivate this samadhi zest-free;
should cultivate this samadhi attended by comfort;
THE 4TH DHYANA:
should cultivate this samadhi attended by equanimity.

Saṅkhitta (Desita) Dhamma Sutta
Jhana is not that difficult if you have the proper guidance.
For Mahaisi method see this answer.