As a relative Skat beginner I face what many new players face: difficulty in evaluating the bidding strength of my hand. Here's a guide which I found on the internet in German and translated.

Count up the points in your hand. If you have 4.5 points or more you have enough strength to bid.

Jack of clubs only 1
Any other single jack 0.5
Jack of clubs and jack of spades 2.5
Any other two jacks 2
Jack of clubs, jack of spades, and jack of hearts 4
Jack of clubs, jack of spades, and jack of diamonds 3.5+
Jack of clubs, jack of hearts, and jack of diamonds 3.5
Jack of spades, jack of hearts, and jack of diamonds 3.5
All 4 jacks 5
Ace, 10, K of any suit 2.5
Ace, 10 of any suit 2
Ace, king, queen of any suit 1.5
Ace, king, 9 of any suit 1+
Any other ace 1

For some examples, if you have all 4 jacks you have a sure bidding hand (5 points). If you have Ace, 10, K in two different suits you have a sure bidding hand (5 points). If you have two jacks and an Ace, 10, K in one suit, you can bid (4.5 points). If you have Ace, 10, K in one suit and A, 10 in another you can bid (4.5 points).

I find this to be a rough guide that is conservative and can make you a bit of a "Mauerer" (someone who always underbids), but as a beginner it's fairly safe. There are many other rules and Skat proverbs that you hear, and many exceptions to all of them. I find Skat to be a very sophisticated game that will take much experience to really learn.