Students are ready to learn blends once they can identify consonant and short vowel sounds and can blend and segment one-syllable words with short vowels.
Your instruction should go from simple to complex. Start by teaching beginning blends, as they are easier for students to hear, read, and spell. You can first introduce the most common beginning blends, saving the tricky 'r' blends ('tr' and 'dr') for when students are more comfortable with reading words with blends. Once students can successfully read and spell words with beginning blends, move on to working with ending blends.
For both beginning and ending blends, start with one-syllable words with short vowels, like grab, clip, and best. Once you've introduced long vowels and other spelling patterns, words such as snack, globe, dream, and sniff are appropriate.
Here's a reminder of where you are on our phonics continuum – what you have taught and what's coming up. This is not the only way to do things, and many programs will teach skills in a different order. That's OK, as long as students learn all the skills.