Depending on where you are with your current bench press ability, increasing your one rep max by 50lb could be a very straight forward or very difficult process.
If you are just starting out and 50lbs would double your current 1RM then the process is quite straight forward, most of your struggles will be addressed through improving technique and giving yourself some time.
If you are already lifting 300lbs then adding another 50lbs may be close to impossible depending on your body size, bodyweight, and level of training expertise.
Whilst the phrase “You can't teach an old dog new tricks” doesn't exactly apply here, it could be possible that your technique is as good as it can be. That being said, the following tips to boost your bench press can apply to the absolute beginner and to the seasoned veteran.
Tip #1. Use Dumbbells to Correct Muscular Imbalances
One downside of training with a barbell is that if you have a muscle imbalance (and you almost certainly do) the stronger arm can take on more of the weight and prevent your weaker arm from catching up.
By using dumbbells you are preventing this from happening as both arms are required to take on 100% of the dumbbells' weight. This may not ever create total balance, but it will help decrease the difference significantly over time.
Another advantage of using dumbbells is that you can increase the range of motion, and work the pectorals more. Bringing the dumbbells lower and wider at the bottom of the movement, and then bringing the dumbbells closer at the top to contract the chest even more.
Tip #2. Perform Negative Reps
Eccentric training, or ‘negative training‘ is a little used form of weight training that is criminally underrated amongst gym goers.
To give you a brief idea of how it works, when performing a bicep curl you have the concentric contraction which is where you are curling the weight up (and shortening the muscle) and the eccentric contraction where you lower the weight back down again (lengthening the muscle). Eccentric training involves only performing the eccentric part of the movement.
So for a bench press, you would choose a weight that you can't press back up and then only perform the lowering of the bar towards the chest. Then your spotter would help you bring the bar back up to the starting position.
The benefits of eccentric training are that it produces more force  increases muscle size (hypertrophy)  and has a significant impact on strength.
The most common mistake with negative training is to over use it, try to limit it to one or two sets of negative bench presses per week (completed after 3 regular sets of bench press). Always use a spotter.
Tip #3. Widen your grip to increase chest activation
Many lifters perform bench press with a shoulder-width grip, this is perfectly fine and will strengthen the chest but will place a lot more emphasis on the triceps.
Now strengthening the triceps is an integral part of bench press training (more on that in the next tip) but when comparing the two muscle groups which do you think would have the ability to generate more force? That's right the pectorals.
Widening your grip will take a lot of emphasis off the triceps and place it on to the pectorals . Remember widening your grip for this exercise is to increase the strength in your pectorals, it will not help you to perform a maximal bench press, for that you need a normal grip .
Whilst we are on the subject, finding the right grip for you is very important when attempting to produce a 1RM. Gregory Lehman (2005) stated that as there is little changes that occur when changing your grip, finding one that suits you personally is best .
Tip #4. Perform Close-Grip Bench Presses
While widening your grip is good for increasing pectoral activation, a good bench press requires strong triceps. Using a close-grip bench press (heavy weight, low reps) is the best way to increase tricep size and strength  which will in turn increase your bench press 1RM.
Tip #5. Keep your Feet on the Ground
This is not a motivational phrase, literally keep your feet on the ground! When people try to perform a heavy bench press it is not uncommon to see them lift their feet in the air, as if doing so will help them raise the bar. On the contrary, this will actually hinder their chances.
The best way to bench press a heavy load is to drive your feet into the floor so hard that you feel the strain in your quadriceps.
This is why you see a lot of powerlifters with their feet tucked so far back underneath them when trying to break records. Because the extra power from their feet is transferred into the lift.
Whilst on the subject, also make sure that your head is in contact with the bench rather than raised in the air. Same reason, it takes away a bit of your power when raising it off a surface.
Tip #6. Train Full Body Rather than Split
Most people who are training in the gym follow a muscle split program, chest on Monday, back on Tuesday, Legs on Wednesday etc … But to get the most out of the bench press you need to increase the amount of times you train it per week.
If you are following a split you will most likely manage to perform bench press once per week (on chest day), whereas with a full-body split you could perform it two or even three times. Schoenfeld et al (2015) found that following a total body program produced significantly greater strength gains than split programs .
To get the most out of your bench press you need to make sure that your technique is flawless, that you are performing it at least two times per week, that you add in close-grip and wide-grip variations, perform negative reps, and alternate between barbell and dumbbell variations.
You also need to be consistent, and make sure that you are constantly pushing yourself, because you will only ever add 50lbs to your bench if you do so.
 Kelly, S., Brown, L., Hooker, S., Swan, P., Buman, M., Alvar, B., Black, L. 2015. Comparison of concentric and eccentric bench press repetitions to failure. Journal of Strength & Conditioning Research 29(4): 1027-32
 Pope, Z., Willardson, J., Schoenfeld, B., Emmett, J., Owen, J. 2015. Hypertrophic and Strength Response to Eccentric Resistance Training with Blood Flow Restriction: A Pilot Study. International Journal of Sports Science & Coaching 10(5): 919-931
 Roig, M., O'Brien, K., Kirk, G., Murray, R., McKinnon, P., Shadgan, B., Reid, D. 2008. The effects of resistance training on muscle strength and mass in healthy adults: a systematic review with meta-analysis. British Journal of Sports Medicine 43(8): 556-68
 Adam Bentley. 2016. Could this arm training program be any smarter? [ONLINE] Available at:https://www.strengthandconditioningresearch.com/perspectives/really-smart-arm-training/. [Accessed 22 June 2016].
 Wagner, L., Evans, S., Weir, J., Housh, T., Johnson, G. 1992. The Effect of Grip Width on Bench Press Performance. International Journal of Sport Biomechanics 8: 1-10
 Lehman, G. 2005. The Influence of Grip Width and Forearm Pronation/Supination on Upper-Body Myoelectric Activity During the Flat Bench Press. Journal of Strength & Conditioning Research 19(3): 587-91
 Schoenfeld, B., Ratamess, N., Peterson, M., Contreras, B., Tiryaki-Sonmez, R. 2015. Influence on Resistance Training Frequency on Muscular Adaptations in Well-Trained Men. The Journal of Strength & Conditioning Research 29(7): 1821-1829