How to read Upanishads?

Reading Upanishads is upon the choice of the reader. Lets have a look what Upanishads says about itself.

Muktika Upanishad listing 108 Upanishads, including itself, reads:

इयं कैवल्यमुक्तिस्तु केनोपायेन सिद्धयति।
माण्डूक्यमेकमेवालं मुमुक्षूणां विमुक्तये ॥ 26 ॥
iyam kaivalyamuktistu kenopaayena siddhayati,
maandookyamekamevaalam mumuxoonaam vimuktaye

Translation:

iyam (इयं) - This
kaivalya (कैवल्य) - Oneness/Sole-ness
mukti (मुक्ति) - Freedom
astu (अस्तु) - There should be
ken (केन) - By what/By whom/By where/From where
upaaya (उपाय) - Means/Approach
siddhayati (सिद्धयति) - Obtained/Perfected/Achieved
maandookyam (माण्डूक्यम्) - Mandukya Upanishad
ekam (एकम्) - One/Single
kevalam (केवलम्) - Merely/Only
mumuxoo (मुमुक्षू) - Desirer (having desire of liberation/Moksha)
vimukti (विमुक्ति) - Freedom/Liberation

Simple meaning:

How this liberation to oneness (kaivalya) can be achieved?
Mandukya merely, liberates the desirer.

Here the meaning of Mumukshu (मुमुक्षू) is not that straight forward to translate. Grammatically it is closer to Desirer, but characteristically it is more closer to Thirsty.
"Mandukya merely, liberates the desirer" might have greater meaning, because reading a book can liberate, is not so convincing.

What after that?

तथाप्यसिद्धं चेज्ज्ञानं दशोपनिषदं पठ ।
ज्ञानं लब्ध्वा चिरादेव मामकं धाम यास्यसि ॥ 27 ॥
tathaapyasiddham chejgyaanam dashopanishadam path,
gyaanam labdhvaa chiradevaa maamakam dhaama yaasyasi

Translation:

tathaapi (तथापि) - Yet/Even Then/Nevertheless
siddham (सिद्धम्) - Accomplish/Achieve/Fulfill
cha (च) - And
gyaanam (ज्ञानम्) - Knowledge
dasam (दसम्) - Ten
Upanishad (उपानिषद्) - Upanishad
path (पठ) - Read/Study
labdhvaa (लब्ध्वा) - Having achieved - derived from labdham (लब्धम्) - Achieved/Obtained
chir (चिर) - Forever/Permanently
dev (देव) - God/Divine
maamakam (मामकं) - From me
dhaama (धाम) - Abode/Dwelling
yaasyasi (यास्यसि) - You will go

Simple meaning:

Nevertheless to accomplish and knowledge, study ten Upanishads.
Having achieved the knowledge, you will go to the abode forever divine from me.

I'll try to explore different Upanishads starting from Mandukya (माण्डूक्य), then other main Upanishads.