Join-as-you-go with Single Crochet is a great technique for connecting individually made motifs while working the last round of each motif.
To complete a sc-join, insert the hook into the indicated stitch (or space) of the current motif, yarn over and pull up a loop (sc remains unfinished with 2 loops on the hook); insert the hook into the corresponding st of the previously made motif, yarn over and pull through all loops on the hook (sc-join made).
Continue working sc-joins across the edge to the next corner.
To join the corner, insert your hook into the same corner space as sc-join of the previous motif, skipping the overlapping corner stitch. You may like to use stitch markers for indicating corners. Continue working in the same manner around the remaining edges of the motif.
Here are some of my patterns that feature the Join-As-You-Go technique using Single Crochet stitches, I hope you give them a try:
If join-as-you-go isn't your preference, you can simply sew the motifs across sc edges instead - Lay out your motifs, then thread a tapestry needle with a single strand of yarn (using the same color as for the last round of the motif) and whipstitch across the adjoining edges.
Explore additional tutorials on Joining-As-You-Go techniques: