We switched from D'Nealian to basic manuscript this year also because the slanted letters and tails were confusing for struggling kids. We use a specific language to describe the handwriting strokes...

We got it from Shaping Literate Minds by Linda Dorn. It goes like this:

a - over around and down
b - d-o-w-n up and over
c - over around and open
d - over around u-p and d-o-w-n
e - across over around and open

ETC...

As you can see, the language is simple and consistent. It has really helped my kinders, and all the teachers are using it now, so the kids will get the same language in other classes and grades. I am modeling how to put the letters on lines now, but I am not requiring the kids to do it yet. Some are ready, and some are not. Something that has really helped to get the right proportion is acting them out like so:

Letters that touch the top line - We stand and put our arms above our heads
Letters that are only as high as the middle dotted line - We put our hands on our hips
Letters that drop below the bottom line - We squat

For example, for the word dog, we say the letters as we act it out:

d - hands over head
o - hands on hips
g - squat

I started this in the past week or so, and even with not writing on lines yet, my kids are getting the letters lined up in correct proportion.

Most kids do want to start letters at the bottom and go up. Every time we practice handwriting we talk about starting at the top. Handwriting Without Tears has a song to the tune of "If you're happy and you know it" to help the kids remember:

Where do you start your letters? At the top!
Where do you start your letters? At the top!
Where do you start your letters? At the top!
If you're gonna start a letter, then you better, better, better
Remember to start it at the top!