I don't encourage all-in betting. But it's up to you if you want to do it, so here's the best advice I can give.
First and foremost: there is no such thing as a sure bet. If there was, everyone would be swimming in Asiimovs. Sure, favorites normally win, that's why they're the favorites, but the game isn't played on paper.
Second: no matter what anyone says, Tier 1 vs. Tier 1 is basically 50-50 chance, regardless of the CSGL odds. These are the best matches to play the odds, i.e. bet on the underdog--however, I do not at all encourage this if you plan on going all-in. The risk is simply too high.
Third: Do your research, and bet smart. Generally speaking, the lesser amount of games in the series, the more favorable it is for the underdog.
However, BO1s and BO2s are also decent opportunities to bet heavy on a favorite if the odds will grant you a decent-enough reward. Which leads me to my next point...
Do not all-in if the reward is not worth it. Personally, if it's anything higher than 70% - 30%, I will not bet heavy on a favorite. For instance, the infamous Fnatic (~90%) vs. Mouz (~10%) bet. If you bet your $30 on Fnatic you'd be risking all you had for an almost worthless return. Sure, it's supposed to be a "guaranteed" win and therefore give you "ez skins" but tell that to the people who bet on Fnatic in that match.
Don't bet just because you can bet. In other words, if there's a game starting between two teams you kind of know, don't feel OBLIGED to bet. If there is some hesitation, SKIP the match and live to bet another day. The easiest way to lose skins is 1) impatience and 2) rage betting.
That being said, the best advice I can give you is just reiterating what I said already: do your research. If you don't have a lot of skins to lose, try to avoid betting on Tier 1 vs. Tier 1. It's just too volatile. Just because TSM always beat Fnatic doesn't mean they will on that particular match you're betting on. Trends exist for a reason, but trends are also not set in stone. You can use these to your advantage, however: for example, the next time TSM faces Fnatic, most will probably bet on TSM making Fnatic the underdog. Fnatic, however, being as strong as they are, have a fairly decent shot to beat them, despite what recent results might tell you.
At lower tiers of competition, the skill-gap between teams can be much bigger than at the highest level (obviously) which makes them the better choice for betting on favorites. Personally, I've had a lot of success betting on NA matches. Despite the volatility of the region and the amount of upsets that happen, I've apparently found some luck with them.
Again, I don't encourage all-in betting, but they're your skins and you can do with them as you please.
Bet carefully, and good luck!