Artur, I played collegiate soccer in the US. We trained for power and strength: 4 days weight training outside of the regular season (off season was daily training on the pitch and 1 game a week; regular season was 2 games per week):
Lower Body Max effort (main lift: reps: 5,5,5,3,3,3)
Upper body max effort (main lift: reps: 5,5,5,3,3,3)
Lower dynamic effort (main lift: warm up with 5,5,5 work sets,2,2,2,2,2,2,2,2)
Upper dynamic effort (main lift: warm up with 5,5,5 work sets,2,2,2,2,2,2,2,2)
2-3 accessory exercises for each main lift usually 4 sets of 6-10 reps per movement Our trainer had us do 30 reps curls and pushdowns at the end of upper body days because we were young men who cared about our arm size =)
Goalies and other position players all trained under the same template. I had a strength training background before starting this regiment, but even for the players new to it, they caught on quickly. We used the same exercises for a few months for the main lifts (box squats, bench). We did some dead lifting and hang cleans, but it was mostly squats, benching, barbell lunges, RDL's, rows, chins. *We started each session with 20 chins, working up to 45 by then end of 1 month. Then we went down to 30 reps with weight. (These are total reps, as many sets as possible to get the rep goal). Our weight training focus was rep quality and rep speed. Trainers allowed players who knew what they were doing to increase weights as they felt, or they supervised the newer players.
As far as effectiveness, we went from a terrible team to winning our conference the year after training in this manner and losing in the national tournament to the eventual champs. A handful of my teammates have enjoyed some form of professional career around the world.
A goalie's explosiveness is going to be a huge asset, so I would say for you to get as strong as you can on the basic barbell lifts, focus on technique and speed, look up Prilipin's rep chart to understand when and how to use rep/set schemes, and look for any type of gains whether by rep or by weight. Consistency is always key.
As far as in season, I know travel can make it difficult, and I know the British seasons are long and lots of games, try to weight train 2-3 times a week. Focus on the important lifts and I would add that you can never train your upper and mid back exercises too much. I hold true the saying 2-3 reps row to 1 rep push. This will help with shoulder help for diving on saves and throwing the ball out to midfield.
When my team was in season, we did not have formal weight training, I continued it on my own (I was a defensive midfielder) and I worked a manual labor job between class and practices so strength was definitly a cornerstone of my game. Many players I trained with and played against had natural strength and ability, but were not "weight room" strong because they were not used to the lifts, but nonetheless most good/great players were strong. The stronger a player, the faster he is. Speed kills, any position.
As far as goalie specific lifts, I would say if you can get used to holding a bar comfortably well in the front squat rack position and do front squats, press and row using different grips (thumbless/false, conventional), and push ups on your fists, it will help strengthen the wrist for impact on saves and punching the ball.
The take away is that like any other athlete, get strong on the basic lifts, have your weight training aid in your speed, strength, recovery, and injury prevention. And focus on your game first and foremost. Most goalies are having careers well into their 30s and solid weight training will help you make it through those years.
Cheers and go Yoevil Town!