2. Openings
- All beginners should focus on fighting for the central squares c3, d4, c5, f4. If you have 3 of them under control, you clearly have an advantage! Therefore, there is a limited scope of openings for beginners:

(1) Most friendly opening for both colours: 1. c3-d4 d6-c5 2. b2-c3 c5-d6 3. c3-b4 b6-a5 4. d4xb6 a7xc5 (http://poolcheckers.com/books/Kaplan/Kaplan_PlayCheckersAndWin.pdf , see game examples from p. 213 to p. 215).
Reversed : 1. c3-b4 f6-e5 2. e3-f4 g7-f6 3. f2-e3 b6-c5 4. g3-h4 e5xg3 5. h4xf2
(2) If your opponent plays passive moves by occupying edge squares a5 or h4, in the beginner levels it is good to play for occupying square c5 (for white) or f4 (for black).
Typical openings:
1. c3-d4 b6-a5 2. d4-c5 (same Kaplan's book, game examples from p. 219 to p. 222).
1. g3-h4 f6-e5 2. c3-b4 e5-f4 3. b6-c5 (colours reversed)
(3) Avoid overcentralization before you had made at least 2 exchanges! The nature of 8x8 board is that central squares can be blocked efficiently by strong edge formations, and if some side makes early overcentralization without exchanges, it can easily result in positions where a player must get rid of overcentralized draughtsmen for equalizing.
(4) Eliminate weaknesses or create weaknesses in opponent's camp.
So, first of all, what is considered as weakness?
First of all, a weakness is any draughtsman which can't make any good move.
At the beginning of the game each side has 3 weaknesses: for white, these are a1, a3, h3; for black: these are h8, h6, a7. These squares are weak, because they have only 1 exit .
Examples:
I don't recommend to play early 1. a3-b4 for white at the beginner levels, because black can immediately squeeze white with simple 1. .. b6-a5, and white must play very cautious moves, otherwise they can lose a draughtsman on b4 very easy.
Similarly, I don't recommend to play early 1. .. h6-g5 for black: 1. c3-d4 h6-g5, 1. c3-b4 h6-g5 are very sharp openings and they are enjoyable only in games between higher level players.
The goal of any good opening is to get rid of 2 weaknesses which I indicated above!
Secondly, a weakness is emptied crowning line (in white's camp: a1, c1, e1, g1; in black's camp: b8, d8, f8, h8).
Many beginners tend to empty crowning line in the opening, yet afterwards their position starts to collapse.
There is a pair of particularly valuable draughtsmen: for white, c1, g1; for black: f8, a7. As a rule, if you can keep this pair of draughtsmen till the initial phase of endgame, you can't lose! However, there are many openings where you are forced to move one of these draughtsmen, but if it happens, you must keep in mind that your opponent can equalize or play for a positional advantage.
Thirdly, a weakness is overly imbalanced distribution of draughtsmen. Normally, you should keep similar number of draughtsmen in each side of the board in front of opponent draughtsmen. If your opponent violates this principle, it means that you should play for attack in the side of the board where he or she has less number of draughtsmen.
Fourthly, a weakness is holes in camp, which in some national schools are also called as "sieve". If you are forced to form some hole in your own camp, one of the highest priorities should be to cover this hole by placing a draughtsmen on appropriate square or to get rid of a hole by means of exchange.
Fifthly, high number of draughtsmen on edge squares is considered as weakness. There are only 2 rational reasons for placing draugthsmen on edge square: first of all, if you are willing to initiate an exchange; secondly, if you can squeeze opponent's camp and paralyze significant number of opponent draughtsman. Here, in lidraughts, I had noticed many Brazilian players whose game plans are based only on memorization of tactical patterns. In many cases, they are going to occupy edge squares (because the majority of shots require some draughtsmen on edge squares), however, they ignore importance of holding control over central squares, and they get punished by running out of good moves.
Sixthly, beginners must avoid early occupation of central squares e5 (for white) or d4 (for black), because they are eventual weaknesses. I know only 2 openings where this early advancement is justified, but these openings are too sharp for beginners. If you play these moves too early, you risk to get an isolated draughtsman. As well, by this kind of move you allow your opponent to make an exchange and get rid of their weaknesses, while your weaknesses are not fully eliminated.

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- Middlegame
Any middlegame is based on looking for favourable and advantageous exchanges, as well as for getting full control of central squares.
With regards to this, the main problem of middlegame is about initiating exchanges.
If you initiate series of exchanges, indeed, you can get very equal position. However, by this you can eliminate your winning chances.
The hardest part of exchanges is that in Brazilian, Pool and Russian draughts you need to examine direction of exchange, because you have exchanges backwards and forwards available. There is NOTHING WRONG with capturing BACKWARDS in these variants, because you create LARGER AMOUNT OF SPACE and you increase MOVING OPPORTUNITIES. If you make exchanges only forwards, you get positions where you are forced to empty first line and, consequently, increase advantage of your opponent. In reality, only in the endgame phase capturing forwards can be more valuable, because at the endgame you should strive to be the first one who crowns some draughtsman into a king.
Apart from central squares, there are some important squares in enemy camp which you should occupy directly or by means of some tactical maneuver: for white: b6, d6, f6; for black: c3, e3, g3. If your draughtsman can stand on them safely, they are doing double job. By time you will notice that sometimes it is worth to sacrifice one draughtsman just for getting a draughtsman on one of these squares, because it allows to force a draw or to increase pressure.

- Endgame
By endgame we understand positions where one of the sides has at least 5 draughtsmen on the board.
You should keep in mind that the easiest wins are ones where you can win without running into a king endgame. It is why there is almost strict order on learning endgames.

1) Learn about OPPOSITION. (See Kaplan's book; I can't present it better).
2) Learn about DRAWING TECHNIQUE in endgame 3 kings vs. 1 king on long diagonal a1<->h8.
3) Learn 4 kings vs. 1 king endgame
4) Learn and endgame where 3 kings control long diagonal and win against 1 king.

This is a minimum for ELO 1300 player, but as I explained above, if you learn to apply this knowledge, you will be prepared for exploring harder themes.

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