I will assume you have chosen your yarn. I would suggest you start off with a simple stocking stitch sweater.
Now you need to knit a swatch.
Once you have done your swatch, you need to wash it and dry it, then give it a light steam press, moving the iron vertically, in direction of stitches.
Now you need to measure it for gauge. You need to find out how many sts and how many rows there are for a 10cm square.
I will base this test sweater on 28st and 40 rws to 10cm.
The following is for a drop shoulder sweater. This will be the basic block from which the set in sleeve , the raglan and saddle will develop.
Decide on the width and length you want to knit.
My sweater will be 62cms wide and 64cms long, without ribbing. The amount of ribbing you want is up to you.
So our gauge is 28st and 40 rws.
For a piece 62cms wide you will need to divide 62 by 10 and then multiply by 28.
This equals 173.6. Roundup to 174.
You will need to cast on 174 sts.
You want the piece to be 64 cms long. So this time you divide 64 by 10 and multiply by 40.
This gives you 256 rows.
You will need to knit 256 rows for your length.
However, our armhole depth will be 28 cms. To find out how many rows that will need, you divide 28 by 10 and mulitply by 40.
You get 112.
Take 112 away from 256 and you are left with 144 rows. So you need to knit 144 rows and then place a marking thread either side to indicate the start of armholes. You leave those markers there until you are ready to join the sleeves.
However, we do want a neck opening. We want the round neck to be 10cms deep. We already know that means the neck opening will start 40 rows from the top.
So we take 40 away from 112, this leaves 72. So we knit 72 rows, and then start the neck shaping. So neck shaping begins on row 73 NOT row 72.
Lets say the opening will be 20 cms. So we already know that means 56 sts(2 x 28 which is the st gauge).
We work only on one half at a time. That means we decrease 28 sts all told for one half of the neck.
I would work it like this:
I would place on hold(MK) or cast off(HK) the centre 30sts. This would leave 13 sts on both sides still to be got rid off.
On a machine I would place 2sts into hold every two rows(on left side) until 25 sts all together on that side have been decreased.
For hanknitters, I would cast off 2 sts every other row until 25 have been cast off.
For MK and HK, I will then knit 4 rws str8 and decrease 1 st, and repeat this until all 28 have gone. Now knit str8 to top.
This is one side of your neck done. Repeat for the other side.
This is the most complicated part of the sweater to do, and it isn't hard is it?
You would do precisely the same for the back, ommitting the neck shaping. HOWEVER, you should still mark stitch 28 on either side of the centre, so you know where to stick your neckband.
If you want the back to be shaped too, usually about 3cms deep, you must get rid fo those 56 sts over 3cms. 3 div by 10 x 40 = 12. So you need to shape over 12 rows.
I would do this:
Put centre 36sts into hold(MK) or cast off (HK). I would then put into hold 2sts ev 2 rows until the 12 rows are done. Your 28 sts for one side will all be in hold. Repeat for other side.
For handknitting, cast off 2 sts every other row until the 28sts for that side are cast off and 12 rows have been knitted. Do the same for the other side.
REMEMBER that you the centre 36sts into hold or you cast them off. So you only have a further 10 sts to get rid of on both side of the sts cast off or held.
Note: 62 cms wide is the same as 24.41" inches.(62 div by 2.54). Your total circumfrance will be 124cms or 48.82"
In practice, I would make the neck opening 17cms wide and 7 cms deep with a 3cm scoop on the back piece. For both male and female garments.