Blackjack, as is any game that involves misdirection and information, has tells of its own. Unlike its distant cousin poker and its many variants, tells in blackjack come from a different source. As you are not fighting other players, you should not be looking at them, but at the dealer, whose hand you need to beat.
First of all, we need to define what a tell is. A tell is an unintentional and often subconscious transfer and communication of information to people to whom that information is being kept from. While players may have tells in blackjack as well, they will never be as important as the dealer's tells. Spotting the dealer's tells may be difficult but this skill can be practice and improved with time. Dealers are people too. Despite being experts at their field and playing more hands than most gamblers ever will, they are still people and people have limitations. It's these limitations that force them to have tells.
Be aware that tells are as varied as fingerprints. Some dealers will have tells that don't show up easily while others will wear the emotions on their sleeves.
A common, yet accidental dealer tell is based on their humanity. People are fallible and make mistakes and dealers sometimes reveal their face down card by accident. One twitch can do it. There are other ways for a dealer to reveal their cards, of course.
The ace is a good example of a card that needs more examination and could potentially lead to another tell. Dealers need to check whether it really is an ace, as the numbers two to six have tops that look similar or the same to an ace. The jack, queen and king provoke a quicker look, as they are very distinct from other cards due to their pattern but are worth the same in any hand.
Watching your dealer like a hawk does not guarantee anything in blackjack and at the end of the day, nothing in blackjack will guarantee victory. A good betting system matched with excellent card counting skills can do more for you than psychologically reading your dealer. You also need to keep an eye on the dealer and figure out which hands this particular dealer plays and of course, how many decks are in play at this table. Try this out and perhaps this will be the edge you need to make your blackjack game a big one.